Rhythm and melody? Well, as you know, the rhythm is much more important than melody and the only thing with the perfect rhythm is metronome. Metronome practice helps you to:
Always be on time!
That’s the main thing why you should always practice with metronome.
Practice at slow tempo!
If you have trouble to play some fast song, slow down the tempo and learn to play a song in that (slow) tempo. Later, you can gradually increase the tempo, until you get to the desired speed. In time, the problem will disappear.
Find metronome software!
There are a lot online metronomes like Bestmetronome, so use it. You can find some of the best free online metronomes in the list of the best online metronomes. But, if you don’t want to practice with online metronome, you can download Zetronome, which is much more than a common metronome and it’s freeware software. Using Zetronome, you can play with various drum rhythms and even create your own drum beat to play with, which is very useful especially for bass players.