1) You may reserve the right to be boring but please don't go there
2) Not every song needs solos. But if it calls for one or two, keep them short and musically interesting. Nobody likes an egocentric showboat always trying to prove how fast they can play for days on end. Don't be a w*nker. Leave your audience wanting more, not demanding you stop playing altogether.
3) Regarding lyrics, corny love songs, songs about trucks, girls and beer have been beaten to death, DO NOT GO THERE!!! Seek out the unusual, off the beaten path subjects or a good story, real or imagined. Also, avoid the sour grapes, angst ridden complaining about girls, politics and mommy or daddy issues. If that's what you obsess over, for God's sake, get into therapy!!!
4) Guard against over-repetition
5) Humor does belong in music
6) Pauses, spaces and dynamics are wonderful components of music. Let it breathe.
7) Given the choice between an antiseptically clean perfect take or a slightly imperfect one with a great feel and vibe, I'll take the feel and vibe approach every time (It worked for Eddie Kramer quite beautifully).
Work to expand your vocabulary both with music and lyrics. Add interest but be careful not to bludgeon your audience with your knowledge.
9) Don't take yourself so damned seriously
10) Yell at imaginary kids to get off your lawn every so often. It's very cathartic.
11) Even if you don't make a dime, creating music is good therapy and keeps you sharp.