The Internet seems to be on a downward slide into an increasingly hostile place. Being bombarded by ads is irritating, slows down browsing and has been used as a vector for viruses and malware. At the same time any privacy is being eroded both technologically as well as legally.
That said all is not lost! There are a variety of things that you can do to curb at least partially some of the most egregious intrusions.
Search Engines
If you want privacy you can't use most search engines. Everything you type will be logged. If you are logged in say with google, for example because you didn't logout of gmail - all those searches will be directly associated with you. Even if you logout there are still mechanisms to track you and associate searches with you.
If you want to scare yourself go to
https://myactivity.google.com/myactivity?hl=en&ent=r&utm_source=udc&authuser=1
It will show, at least some of the data google has tracking you. I purposefully avoid google - but was still shocked what it had listed.
Anyway to cut to the chase I would recommend using duckduckgo for the majority of your search requirements.
It's fast it's results are good. They are perhaps not quite as good as googles. And their image search also doesn't seem to be as mature. That said I've been using for years now and think it is solid - and they honor your privacy. In practice I use duckduckgo for the majority of my search requirements - and very occasionally I will try google or bing if I think I'm not getting the best results.
I would recommend making them your default search engine in your browser. You can typically do this by going to the duckduckgo website and there is an option on that page to make it your default search engine.
Browser Extensions
Most of the following items are addons/extensions for your browser. Overall I would recommend using the firefox browser. The chrome browser from google is an impressive piece of tech - but is not as good from a privacy perspective. I'll talk a little more about why later. I would not recommend Internet Explorer, Microsoft Edge or Safari. Most of the items below are addons (for firefox) or extensions (for chrome). All are free - if you like them and use them though I would recommend donating something so the developers can continue and improve the software.
Note that in sections below - clicking the link will typically take you to the place where you can install the plugin directly.
For firefox go here
https://addons.mozilla.org/en-US/firefox/
You can look up addons here or use the links below and add 'add to firefox'
In chrome you can find and add extensions from... https://chrome.google.com/webstore/category/extensions?hl=en-US
lookup the extension from below (or click associated link) then click 'Add to chrome' and then 'Add extension'.
Ublock Origin
First 'ublock origin' it's main purpose is to stops ads. Which not only makes using internet faster/nicer - it removes a vector for viruses.
https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/?src=ss https://chrome.google.com/webstore/search/ublock%20origin?hl=en-US
Privacy Badger
Privacy badger is from the EFF and makes tracking you as you move between websites more difficult (although still possible), and reduces the amount of information that a website can see on you.
https://addons.mozilla.org/en-US/firefox/addon/privacy-badger17/?src=search https://www.eff.org/privacybadger
Https Everywhere
Https Everywhere makes it much harder for a 3rd party, say comcast, or any computer between you and the website/service you are accessing to see what you are doing. Note that comcast can still tell what website you are connecting to - just not what your doing there.
https://addons.mozilla.org/en-US/firefox/addon/https-everywhere/?src=ss https://www.eff.org/https-everywhere
No script
Ok - so this is where things get a bit more difficult. All the plugins/addons I've listed so far are essential pain free. You install them and your experience of using the internet becomes safer, faster and more private.
Many websites execute 'javascript' code on your computer. This code enables websites to do lots of nefarious things - from tracking you across websites, to tracking where your cursor moves whilst you are on a website, to worse - as a vector for viruses. It can also be used to make websites load faster, and have more interactive features. Some websites do not work without javascript.
No-script turns off javascript by default. It then allows you to turn on which servers can run javascript on your machine. So this is great from the point of view you have much more control on who runs code on your machine. On the other hand it can be a pain, because it's not uncommon that when you go to a new site it will have problems - and then you have to turn on manually what you want to make it work.
Many people don't like this extra friction. No script isn't available for chrome, but is for firefox.
Only install if you are really serious about privacy! And your prepared to have the extra friction of having to enable/disable what each website can do. I would not recommend installing if you are not fairly tech savvy either.
https://addons.mozilla.org/en-US/firefox/addon/noscript/
Random Agent Spoofer
This addon is only available on firefox. This tool also causes some friction - so I would only recommend if you are fairly technically savvy and concerned about privacy.
When your web browser gets information from a website - it also informs that website with information about your web browser as well as the operating system you are using.
The combination of this data can be used like a 'finger print' to follow you around the internet. A malicious website can also use knowledge of the precise browser you are using to attack you - as certain weaknesses are only available on certain browers.
This addon allows you to change the data that is sent to the website. Typically I will choose a different operating system, and a different browser (or older version of the type of browser I have).
Note that some websites may be confused by this. If you say you are running on linux and you go to a download page it might default to downloading the linux version when you need the windows version. Moreover some websites use specific features of browsers, and by spoofing them they send the wrong information. In either case you can disable the spoofer for that website.
https://addons.mozilla.org/en-US/firefox/addon/random-agent-spoofer/
Handling problems
Most of these plugins are effectively friction free. Some are not though - no script and to a lesser extent random agent spoofer. That said there can be problems. If you go to a website that you know works and is safe you may want or need to disable some of these tools.
Generally the extensions/plugins add new icons in chrome/firefox all on the top right (to the left of three vertical dots). You can use these to switch on and off, and alter settings. If you click the icon typically the main option is to disable the tool is at the top.
Sometimes the option is to disable temporarily or only for a specific site. It makes sense to only disable in the most limited way such that you retain the most protection. I generally only disable temporarily and if I don't I only disable for a site. It's generally not wise to disable in general.
Finally I always have two browsers available to me. Typically I'm in hardened firefox. But I keep another browser such as chrome or internet explorer available, such that if something is not working and I think it should - I test with a browser without the protections. I will only do this very rarely and only if it's a site I know isn't malicious.
Windows Telemetry
If any of your machines use windows 10 - microsoft has a heap of spying mechanisms. Some are controllable in settings - but many inaccessible. To block these you can use spybot anti-beacon. Download and install on machines that have windows 10 and switch off what you don't want. Microsoft has added some spying to Windows 7 and 8, so you can use it there too, but its Windows 10 that is the worst by far.
https://www.safer-networking.org/spybot-anti-beacon/
Browsers
So at the start of this article I recommended firefox. The main reason is it has a large selection of privacy and security related addons, performs well, is available on all major platforms and is backed by a not-for-profit that has users interests generally at heart.
Most of the other main browsers are backed by huge corporations who are in a race to the bottom on how much information that they can extract on you. I think google chrome is a fine browser, but it sends an awful lot of information to google - so I can't recommend it.
You can use chromium which is the open source version of chrome. Unfortunately and unsurprisingly google is not keen on your using chromium over chrome so they make it hard for you. To download chromium for windows you can go here.
The problems with the rest are either of poor security, poor plugin/extension support or do not conform well to web standards (Internet Explorer).
Be Careful What You Type
As a word of caution by default everything you type into a website can be and often is captured. If you type something, and then delete it - it is likely on most websites it has been captured. So if that's a problem you should construct your prose in word, notepad or some other text editing software, and cut and paste into browser when you are done.
Other Resources
The EFF has a whole section of their site devoted to privacy.