The Tits are vocal all year round though they become more clear and assertive in the spring and summer. There is often considerable variation in their songs and some species' sound similar to one another. The Blue Tit's song is quite distinctive and difficult to confuse with other species. Learn this and the next two will be easier.
The Blue Tit is the ubiquitous tit and so provides most people with the opportunity to learn its song and calls. The high pitched trilling song is often written as "tsee-tsee-tsee-chu-chu-chu". Baloney, I hear you say! May be, but listen to the examples and you may be convinced. If not, think of your own mnemonic and share it with the rest of us.
In some respects the Great Tit is the easiest song to learn, but they also have a great many calls that challenge even the most experienced bird watcher. Anyway, back to the song, this is the renowned squeaky bicycle pump, "teacher-teacher". This is loud, high pitched and sometimes very persistent. This song is higher pitched than Blue Tit but sweeter than Coal Tits'.
The Coal Tit's song is almost as loud as the Great Tit's but not as sweet or persistent. It is also very similar to the Great Tit's, but sounds more like "pee-chew, pee-chew" or "titcha-titcha". With a little imagination, you can imagine it trying to shouting its own name "coa' tee, coa' tee".