1. don't stand still
2. attempt to aim at the head
3. dont go running around with your smg as your main weapon.
4. jarate+bushwaka is your best friend
5. if you cant aim, dont use the bazaar bargain
6. if you cant get head shots use the machina, you'll get an instant kill on almost all classes if fully charged.
7. dont die
soon to come, unicorns guide to being a competent demoman
(i capitalized unicorn :O)