We've been talking about "S.M.A.R.T." goals. For instance:

S-pecifc [I need to learn my new band's arrangements of 40 songs, plus vocals on 12 of those]
M-easurable [I need to learn them well enough to perform them]I'll measure my success against the approval I get from my bandmates in our weekly rehearsal, and at the gig.
A-cheivable [I can do it - I've played 80% of them at one time or another]
R-ealistic [I want to do it, and I need to do it to be qualified for the gig]
T-imely [Our next gig is in early December, 6 weeks away]

Promise yourself a reward for acheiving your goal. Now, in the case of musicians, most of us feel that just having the opportunity to play is it's own reward, but when you set goals, it's a good idea to set a