The first thing to know is that everyone has an odd sense of rhythm… but in fairly predictable ways!
Take a fairly slow beat, like, 60 beats/minute (bpm), 1 a second… most people will expect the next second to come sooner than it actually does. And with a fast beat, usually above 110, people expect the next beat to be later than it actually is. Many songs' tempo, and a good tempo to start learning with, is usually in the mid-80s.
Here’s the interesting thing about that - when you turn on a metronome at 88, and start trying to play along with it, it doesn’t seem to beat steadily. It will probably seems to slow down a bit. And then speed back up, and then level off.
The reason is because of the way you anticipate the next beat that follows. So, there’s a trick to using a metronome to practice keeping a basic steady beat.
To start with, you don’t need much equipment besides a metronome (I’m sure there are programs you can use on your computer, but make sure it can click instead of just beep, and it really must be able to let you set its rate, in beats-per-minute.) You can use something appropriately drumstick-like (even a pencil will do) that you can tap a surface (one that won’t be damaged by it, of course) in time with it. Choose something lightweight and stick-like that you feel you can control well, so it isn’t causing you additional problems in rhythm.
But don’t start tapping just yet! Just listen for a little bit. Turn it on at 88 BPM, and listen to it 'slow down', and then speed back up, and when you actually feel like it’s going steady, then join in with the beat. If you’re not sure, just give it 20-30 clicks or so. It’s much easier to join in on something that’s already going, than it is to start with no lead-in at all. (It takes bands a lot of practice to be able to use a simple count of four and still play at the right time three beats later. Mediocre bands often can’t agree on a tempo for the first 8 beats or so.
What you’ll find is that after a while, you might occasionally tap the stick, and not hear the click from the metronome. Or, if the metronome is even slightly louder than your tapping, you won’t hear the tap instead, in which case you should try to turn down the metronome’s volume, or find a different surface to tap on.
Because of the way sounds work, there’s a type of effect called "masking" - if you hear two percussive sounds close enough together in time, you won’t perceive both of them. You’ll just hear whichever one is even a tiny bit louder. So you know you’re right exactly on the beat if you actually can’t hear the metronome while you’re doing it. (Okay, this is a little white lie, but without getting into some complex psychoacoustics, this explanation is good enough.)
And that’s the first thing to do to practice it. Go for less than five minutes, then take a few minutes of a break, then try it again. It won’t help to spend more than 20 minutes or so in a session, or more than three sessions a day. (This might vary from person to person, but the learning process would be the subject of another article…)
That’s step 1 of developing a better sense of rhythm. More to come!