From my experience it takes at least a year of on-and-off playing to get truly good at TF2.
Main tips: If someone with your team colors is acting suspicious - don't save ammo shoot him, preferably with a secondary if possible.
NEVER stay still, especially if you're heading towards a sniper. Jump, go left and right randomly etc. When within melee range and having a melee fight dance around your enemy, jump - go left, right - be unpredictable so they can't hit you back, crouching for half a second then running off again can be useful.
There are plenty of class related tips I could give you, what classes do you prefer so far?
Main tips: If someone with your team colors is acting suspicious - don't save ammo shoot him, preferably with a secondary if possible.
NEVER stay still, especially if you're heading towards a sniper. Jump, go left and right randomly etc. When within melee range and having a melee fight dance around your enemy, jump - go left, right - be unpredictable so they can't hit you back, crouching for half a second then running off again can be useful.
There are plenty of class related tips I could give you, what classes do you prefer so far?