Twitter lists are a really powerful tool, but one that lots of people don't seem to know about. Basically you can add an account to a list that you create. You don't need to follow the person, but it's really easy to just add people when they start following you. Start off by going to https://twitter.com/your_name/followers and you'll see a list of people that are following you. Each person will be in their own little box with a 'Follow' option and next to that, 3 vertical dots. You can choose to follow the person (obviously) and you can also click on the 3 dots. This will give you an option of adding people to a list - 'Add or remove from lists'.
If you click on this you may find absolutely nothing - this will be the case if you haven't set a list up yet. Simply choose the option to create a list and then call it whatever you would like to. For example, I have lists for 'UK Librarians', 'Search Engine accounts' 'Libraries' 'Friends' and so on. You can make the list publicly accessible or you can keep it private. Once you've set up a few of these lists you can then start adding people to them. One account can be added to multiple lists if so desired, so I'll quite often add someone to my UK librarians list and also my Schools library and librarians list as well.
Unfortunately you can't just tweet TO a list, but you can see tweets FROM that list. That's really useful if you've spent the day being busy and just want to catch up on what a particular segment of the people that you've listed have been tweeting about. You can either do this directly from the Twitter interface or you can add lists to packages such as Hootsuite. Simply click on your avatar at Twitter.com and the second option will be 'Lists'. Click on that, see the lists you've got, click on one of them, and lo and behold - just tweets from the accounts on that list.
Of course, you'll quite possibly be on some lists yourself. Click to go to your profile and in the top menu is a section called unsurprisingly 'Lists'. Click on that, then choose 'member of' and you'll see what you've been added to. What you can also do, which is very neat, is to subscribe to any of those lists or others that you find. This means that you don't have to actually follow all of those people - the list will appear in your own collection (though of course you can't add people to it since you don't own it), but you can then just see the tweets from the accounts on the list. So my UK librarians list currently has 1915 accounts on it and you can find it at https://twitter.com/Philbradley/lists/uk-librarians and if you want to, you can subscribe to it. It currently has over 300 subscribers - so this means that you can automatically see what these accounts are tweeting without having to follow them all.
If you have any questions, do post them. However I'll try and answer a few before we start. You can create as many as you like, with as many members as you want. I do seem to recall a limit of 5,000 but I could be wrong on that. You can keep them private or public. I don't think you can force not being on a list, but of course you could ask the list owner to remove you. You're entirely free to add people, even if you're not following them. Your lists, your choice.
I've got lots of lists - you can see them at https://twitter.com/Philbradley/lists/ and feel free to subscribe to and use any of them that you want to. The ones that might be of particular interest are:
UK Librarians and this is my guesstimate from people who follow me that they're a)library folk and b)based in the UK. I may be wrong on either or both counts!
School libraries and librarians is a list of school library accounts and school librarians where I've been able to identify them as such. Global in coverage.
Libraries from around the world which could be public, academic (university etc), specialist - anything except school.
Library Associations is a list of professional or voluntary groups that are obviously library related.
There are plenty of others, many of which won't interest you, but feel free to take a look.