Two questions:

1. I've just started soloing over some of my favourite tracks... at the minute however, I'm relying on sheet music books to find out which key a song is in... I'm guessing there must be another way???

2. I'm currently soloing using the major and minor diatonic lead patterns, but how do I know whether a song is in a major key or a minor? Can I tell from the key signature? If the key signature has sharps, does that mean it's in a major key? And would a song with flats therefore be in a minor key?

thats is kind of hard to explane for me with out showin u . many times in sheet music the but u can look at both the first and last chord in the song to come up with the Key , i have some cheat sheets i am looking for to explane it better to you if i faind them i will give u some great ways on finding the key

A little music theory knowledge can go a long way to helping you work out keys both with sheet music and without (via your ear).

If you have the sheet music for a song, knowing the cycle of fifths will really help. The cycle is C G D A E B Gb Db Ab Eb Bb F. Each major key has a relative minor key that shares the same number of sharps/flats.

Example:
C major = C D E F G A B C (no sharps/no flats)
A minor = A B C D E F G A (no sharps/no flats/same notes as C major, but with A being the root note). Using the cycle above, the relative minor is always the third note away from your root (ex. C to A - A being the third note after G and D, G to E, D to B, etc)

The cycle also follows a pattern of increasing/decreasing sharps and flats as you move through it. (# = sharps b = flats)

C - 0 C D E F G A B C
G - 1 # G A B C D E F# G
D - 2 # D E F# G A B C# D
A - 3 # A B C# D E F# G# A
E - 4 # E F# G# A B C# D#
B - 5 # B C# D# E F# G# A# B
Gb - 6 b Gb Ab Bb Cb Db Eb F Gb (careful here - can you see why?)
Db - 5 b Db Eb F Gb Ab Bb C Db
Ab - 4 b Ab Bb C Db Eb F G Ab
Eb - 3 b Eb F G Ab Bb C D Eb
Bb - 2 b Bb C D Eb F G A Bb
F - 1 b F G A Bb C D E F

Knowing key signatures (how many sharps/flats) will let you know one of two possible keys, a major key or the relative minor key.To determine this, look at the chord progression and see what type of chord is most prominent, major or minor. If it is major, the tune should have a stable sound (some would say a happy sound). If it is minor, the tune will have a darker/sadder sound. Once you've isolated the sound, you can then pick from the major/minor scales you know to solo.

Learning a key by ear, while much harder to do at the early stages of your playing, is an outstanding way to practice. All you need to know to get started is two scales, the minor pentatonic and the relative major scale (ex. A minor pentatonic to C major). Don't get me wrong, the more scales and arpeggios you know, the better you are at finding key centers, especially tunes with multiple key centers. But to start, you just need those two.

First, start the song...

Second, play your minor pentatonic scale up the neck one fret at a time. If any notes sound sour or sound like they do not fit, move on to the next position.

Once you have found a position where the minor pentatonic works well, check yourself by using your major scale up a minor third (3 frets up if you play guitar) ( ex. move from A minor pentatonic to C major).

If you've found the right position, all seven notes of the major scale should work as well. Again, any sour notes and you will still want to keep checking. Some keys are very close with only one note difference (G and C for example - F# is the only different note between them).

Finally, like you did with the sheet music, listen to the mood of the song. Is it dark and sad? Then think minor key (use your minor pentatonic or Aeolian mode as a starting place for soloing). If the song is not dark/sad, think major and go wild with the major scale or Lydian (a nice choice with the raised 11).

Thanks for your help.