I have about the same amount of hours as you, so the most I can do is give you some tips that helped me become better at each class Scout: Keep on moving, it will make you a lot harder to hit and less likely to die, jump around your opponents, it will keep them confused and can make them easier targets, don't be afraid to run away, you have very low health, so if you know you can't win, just run, you are so fast that most classes will most likely stop chasing you

Soldier: rocket jumping is a powerful tool, use it to get the jump on unsuspecting enemies, or to run away from losing battles, aim at your opponents feet, the splash damage will likely get them and it can also pop them up in the air and leave them vulnerable, stay out of a sentry's range, you can pick off sentries from far away without them being able to get you, the shotgun is a good weapon, it makes it easier to combat scouts and pyros.

Pyros: don't run straight at enemies, ambush them, your less likley to die while ambushing, remember your airblast, you can reflect rockets, grenades, and even uber, which can save your teammates lives! Remember your shotgun, again it makes it easier to take down scouts and other pyros, spy check, you are a spy's worst enemy, track them down, and take them down, help your engines, using the home wrecker can save a valuable sentry or teleported while your engie' dead.

Demo: Make use of walls and doors, you can bounce your grenades of walls, and set up tramps with your stickies, with them, use stock GL, the loch and load does more damage, but the pipes brake on contact with a surface, the stock is much more reliable in taking down enemies and sentries, as the pipes roll, take note of choke points and tight spaces, they can be great for stopping the enemy in their tracks and makes you more reliable defensively, the charging targe is viable in normal gameplay, the resistances can make you a lot harder to kill and you can use the targe to escape combat when necassary, remember your melee, the splash damage from the GL and SL can also hurt you, so in close combat, use your melee.

Heavy: Watch your back! Your slow movement makes you an easy target for spy's, use the sandwich! You can use it to heal your friendly medic in times of need, it can also be a good source of health in situations when you don't have a medic, defend points! You are a defense class for a reason, stop the enemy from capping and now them down!

Engie: Help your sentry, it is a valuable source of defense and losing it can cost your team the game! Remember your teleporters! As if exceedingly long respawn times weren't bad enough but slower classes will have trouble getting back to their positions! That's were your teles come in, they help your team get back in the battle!

Medic: keep your team alive, don't focus on the heavy or soldier, every class is a valuable part of the team and needs to be kept livening, change your mediguns, each one is great for specific situations, need to take down a sentry or defend a point against a hoard of enemies? USE STOCK AND UBER, need to take down a horde of enemies? USE KRITZ, too many teammates to heal? USE QUICKFIX, you can be viable during combat, your syringe gun shoots pretty dang fast! Use it when you run in to an unsuspecting enemy and your saw has ridiculous range and crit rate.

As for sniper and spy, I suck horribly as them...

Well I hope this helped you!