So as basically every one knows I’m learning the bat country solo slowly. I’m using a metronome to help but my issue is I have no idea how far to bump up the bpm and how to know if I’m ready to play a bit faster. Any tips?
If you can play it perfectly at the bpm you are currently at, then that is a good indicator to try and bump up the speed little by little until you can't play it cleanly. Once you play it cleanly at the new speed, you bump it up again. Rinse and repeat until you are at the bpm of the song.
I agree with what Steven said. You can also try the Troy Stetina speed method. He goes 5bpm up, when it's too fast go 3bpm down. You can also go up by one and slow down by a few bpm. Either way, slowing it a bit down when I reach my limit works for me personally. It can also save you from frustration and perhaps helps you get comfortable with different tempos too
To be honest, I use to have a big ego when it came to increasing speed. I use to think "Okay I played it great 5 times now I can move up the tempo" or I would say "Okay I've played it for a minute I'm ready to move up the tempo." 99% of the time, I wasn't ready, even doing all of those things I wasn't ready.
The biggest thing about playing slow is muscle memory. And you cannot play fast without muscle memory. You can't. Plain and simple. The moment you are able to disengage the connection between "thinking about what you're playing" and "playing what you're playing", and you let it become automatic, then you are ready to build your speed by increasing the tempo.
If you cave in to the urge of increasing the tempo to judge your improvement, you are doing yourself a huge disservice. Speed should never be the goal. Muscle memory and autonomic playing should be the goal, because everything else will fall in line.
Otherwise, you will struggle with the sensation of always having to "fight" to keep the speed up. You don't want that. You'll hurt yourself. Great job for still working on it!