For Improvising it's crucial to know the Key of the music.
The most common Guitar Keys are C, G, D, A
So practising those Scales with their Fretboard Patterns
is a good idea.
The Key Signature, those sharps [#] and flats [b]
at the beginning of the Music Stave, will indicate the
key the music is in. [more later]
No sharps [#] or flats [b] shown? Then the key is C major
One sharp [#] shown and the key is G major [G A B C
D E F# G]