A couple of thoughts.
You don’t need to strengthen your hands to play bass. If you’re experiencing hand fatigue there’s a good chance you’re fretting and/or plucking the wrong way and possibly opening yourself up for an RSI down the road. It’s a risk anybody pursuing the self-taught route encounters and maybe the single biggest reason why getting at least a few lessons under the eyes of a real live instructor can be so important. Lacking that, sitting down with somebody more knowledgeable who knows what they are doing can be invaluable in evaluating your technique and stopping any bad practices before they become habits.
Same goes for fatigue if your bass isn't properly set up. Set ups are easy to do once you know how and do it a few times. And fortunately, there’s plenty of good videos and articles to walk you through what’s basically a 3-step process. So if you haven’t set your bass up yet, do it ASAP. And if you don't know how, take a moment to learn how to do it.
Second point: don’t overdo practicing. 60 minutes of concentrated daily practice is plenty. If you want to play more than that, try applying what you’re practicing to playing actual songs. I’ll sometimes sit with a bass unplugged and play along with the music in show a I’m watching. But I do it more for the ear training (finding a song’s key quickly, proactively anticipating chord changes, getting a better feel for styles and genres I don’t usually play, etc.) than for bass playing per se. Because to become a better bass player you can’t just focus exclusively on your instrument. You need to engage your whole self in music in the broadest sense. So don’t let yourself get so hung up on bass playing that you neglect the bigger picture as part of your musical education. (Minor note: if you do any similar exercises where you’re just sitting around playing, always pay attention to your posture. Not doing that can lead to bad technique and bad habits.)
Most important- anytime you pick up your instrument, have a plan
and a goal. It can be as formal as: “I’m going to master this lesson in Ed’s book during this session.” or as loose as: “I’m going to see how quickly I can find the key and play along as best I can with the music in all the commercials of this show I’m watching. But either way always have some plan and some goal in mind. Do
not just noodle around idly if at all possible.
Another good exercise is playing with your eyes closed. Take a simple I-IV-V blues progression and get comfortable playing it with your eyes closed.
Next it’s time for what I call “target practice.” Think “blues in E-major.” Now with your eyes closed grab the root of the first chord and play it. Open your eyes and look. Are you fretting the right note? If not, correct it and play through the progression one full time, then close your eyes, drop your hands, count to ten, and and try again. When you can do it three times in a row and get it right, pick a different key. Rinse and repeat. That’s good for muscle memory, ear training, learning the fretboard, and getting comfortable playing when you can’t see the neck. Because there will (not may - but will) come times on stage where you’ll get plunged into total darkness or be temporarily blinded by some unexpected glaring light source. And the ability to continue playing until you can see again is a valuable skill to have under your belt. So time spent playing blind and doing target practice is going to be time well spent.
There’s lots more, but the above is plenty to think about for starters.
Luck!
