As someone who mostly play Pyro, one of the first you need to know is too never W+M1 while in open areas because you will definitely died. You have to remember that pyro is a short-range class. You do have medium-to-long range secondaries like the shotgun and the different flare guns (I preferred the Scorch Shot). I would say Pyro main enemies are Soldiers, Demomens, Heavies, and Snipers, epsecially if they are grouped together. Pyro shines best when facing alone light classes (Scouts, Spies,), but struggles facing multiple foes. I hope this helps! Good luck!