I took a long break from bass for about half a year so I could focus on my trumpet playing and I need to get my chops back up to scratch. The majority of exercises I've seen are geared to developing speed. I don't care about speed, I'm no Sheehan - I wanna get rhythmically tight. Know any nice exercises?
Using garage band or similar software, record yourself playing to a metronome. Attempt to play consistently ahead, behind and on the beat and use the editor to see how you did. Use the midi editor or the waveform editor to see how playing in those temporal locations should sound. Compare it to your playing. Then, see if you define "tight" in one of those terms: playing ahead, behind or on the beat. Play complex rhythms, or irregular meters, testing yourself, by, e.g., playing the Rite of Spring at tempo.
Depending on the type of music you like -- play along with your favorite recordings. Play along to Tower Of Power if you want to get super tight -- or try almost Motown recording for that soulful tight pocket. When first working out pop & rock grooves I played along with Police & Sade records. I really like Rage Against The Machine for doing the funky rock slap bass thing... Now I play along with Miles, Trane, Bird, Cannonball... : )
If you want to get to play real tight grooves then here's what I would reccomend get your metronome, set it at reasonble tempo, play 16th or whatever, and accent then 1, then accent the 2, then the 1-and, ect I reccommend taking this as far as you can as slow and fast as you can with the greatest and least dynamic difference as you can
Along with the other metronome posts.... This may sound a bit strange, but put your bass down, sit with a metronome set at a reasonable tempo (60 bpm is fine) and clap your hands with the click. You know you're getting where you need to be when you can't hear the click ....consistently, over several measures. FWIW, metronomes with an actual click sound (as opposed to a "beep") work well for this. When you've mastered that, at various tempos, set the click to play on the 1 and the 3 and clap out every beat. Then set the tempo to only click on the 1 ....and clap out every beat. You still need to be hitting the 1 with the metronome. With your bass, set the metronome on the 1 and 3 again, play your favorite shuffle or blues scale, and make your metronome swing. It may sound static or artificial at first, but work on feeling the space between the click and what you're playing. It's very cool when the metronome doesn't seem like a metronome anymore.