I have a few chords down and want to master some solos but the problem I have is finger positioning.

I read the tab and can work out where to play the note but my finger positioning is not good and may be stopping me from building speed, changing note well, and playing more fluently.

Any advice on this?
I'm assuming by finger positioning you mean certain nuances like the angle against the fretboard, etc.

I generally try to mute most, if not all the strings I'm not playing. At the very least, the strings higher than the ones you're playing. Ideally this means my fingers are flat against strings.

The thing about finger position and speed is that they usually don't correlate. What you want is correct muscle memory and minimal tension. In that respect, you want to do two things:

1) Focus on moving your fingers away from the fingerboard the smallest distance as practically possible

2) Fretting the note with the least force possible to let the note ring out clearly and loudly.

Other than that, I think you should stop doubting yourself. It's hard at first, but keep at it, learn things slightly above what you can play, and you should be able to progress well.

(Also remember that the picking hand is equally, if not more important if you want to get to some serious speeds.)
Do you mean which finger you should fret the notes with?

As always it comes with practice I would consider watching other people playing the solo to get an idea.

I would say generally though try and keep a one finger per fret hand position, practicing scales would help with getting comfortable with that and look ahead at how it moves around the fretboard and make sure your hand is moving into the right position.

It might help you to print out the tab and write the fingering above it to remind you in the beginning.