Get a metronome. Today.
Human beings have this knack for tricking ourselves into believing we have something all figured out. One of the biggest obstacles this little quirk presents to musicians is that we aren’t always aware of the beat. We slow down or speed up when it’s convenient or cut beats out of a song entirely, usually remaining blissfully unaware of the fact.
A metronome is the silver bullet cure for this problem. Be warned, though; it’s your worst enemy as well as your best friend. The metronome won’t be reasoned with and won’t stop making it painfully obvious when and where you’re butchering the rhythm.
Sound like a pain? It kind of is, but it ultimately fine tunes one’s sense of beat and makes your rhythm tighter and more precise. As they say, no pain no gain.
I prefer a mechanical metronome with a wind up crank for general practice. Sure, electronic ones are a bit cheaper and a metronome app will do in a pinch, but having the visual advantage of seeing the pendulum conduct you as well as the satisfying tic-toc (as opposed to a harsh beep or phony sounding woodblock) makes it seem more soothing somehow.