Uh i've never really been in a situation like this cause while i am in a band we all have some sort of formal music related background so when we started working together we already had our bases covered yk but train playing with a metronome since the beginning, it may be the bane of u guys at first but it's really important so u learn to play with other people. This is especially important for the drummer, but applies to everyone. Also lock in a bit on the music theory part. U don't need to become the biggest music theory nerds ever but the basics like time signatures, how different keys work, how to pair up chords etc is extremely useful when playing with others cause if you make mistakes while playing then u can recognize and fix them more quicky and intuitively. Train you ear too, being able to pick up things after listening to them is a very nice skill to have in those settings too. Finally, the solo guitarrist should get familiar with pentatonic scales, considering pretty much every guitar rock solo is some sort of pentatonic progression, so knowing how to play those will make learning solos easier and faster in the long run. And if u pair that up with a trained ear and some theoric knowledge then it becomes simpler to improvise and come up with things on the fly ;)
I wish I had tips for singing but i fucking suck at it too XD so uh training ur pitch recognition is good for that also remember to always warm up especially before long sessions (this one applies to the instrumentalists too, u guys don't want to get tendinitis or anything) and if u're doing something that hurts stop cuz u're prob doing it wrong and it will damage your vocal chords.
Also don't forget to have fun, that's the most important part :D