Many people think of 1, 2, 3, 4 as a kind of "ready, steady, go"... and maybe counting in that way is better than not at all. But often, that type of counting in is actually completely wrong. Especially when practicing a song and counting into a specific part of the song.
Let me try to explain it as simply as possible.
Why do we count in? It's not just so everyone knows when to start – it's also so everyone starts at the same tempo with all that it implies. Surprisingly many people don't think about that.
You can see the count-in as a guide, an instruction on how the rest of the song should be played.
How much do you need to know about measures, for example? It doesn't hurt to read up, but an interest in music goes a long way. Simple songs manage with simple count-ins. Or do they?
Let's imagine a common song. The Christmas song "Jingle Bells". Many might not think about, know, care about, or understand that it's played in 4/4 time. But most people can count to four when the song begins, and that's usually enough.
So, counting to 4, at the same tempo you plan to sing "Jingle Bells", should work perfectly fine.
Anacruses make it difficult. An anacrusis is when you sing a phrase before the first beat of the measure arrives. Let's stick with Christmas songs. "We wish you a merry Christmas" is an example of something you cannot start singing with a regular count-in. "We" is considered an anacrusis. Even those unfamiliar with these words and concepts will likely agree that the stress is on the word "wish". So, when you count in this song, you only manage to count to 3. The anacrusis, the word "we", falls on beat 4. It becomes; 1, 2, 3, "we".
There are longer anacruses. Let's count in the song "Blue Christmas". Here, the stress/first beat is on the word "blue". The whole "I have a" is an anacrusis, so here you only manage to count to 1.
1, "I have a". An anacrusis where you only say 1 is not helpful to anyone, so here you can happily count twice. 1, 2, 3, 4, 1, "I have a".
Then, of course, there are plenty of exceptions and special cases. This can involve songs in odd time signatures and/or those that change time and/or tempo. For example, there are phrases/songs that begin with a rest. There are songs and phrases that (with an anacrusis or) do not begin on a so-called syncopated beat, in the middle of two beats. There are songs that both begin with a rest and on a syncopated beat. So, there are songs that are not entirely easy to count into.
The examples above are partly constructed, partly exaggerated. Very often, the way to count in is completely natural. The songs you count in are usually songs you already know. If you are unsure, you can count silently (or loudly, for that matter) while the song is playing. Then you get a sense of both the song's time signature and tempo, and you can deliver a clear and good count-in when it's time.
Many times, you help others by counting to 4 (or whatever it is) two or more times. Sometimes it can help if you first count one measure at half tempo and then at regular tempo. 1... 2... 1, 2, 3, 4.
Sometimes it can help to clap your hands, snap your fingers, or similar. At regular tempo, at double tempo, or whatever you find natural.
Yes, because it's not a "ready, steady, go!" we should shout. No, it's about showing and guiding your fellow musicians – and often yourself – in a short time: What tempo the song is in, and exactly when we start.
