Early Game

Poke your opponent on lane and always attack him when he attacks you. You have 1 more additional dmg at level 1 in 1vs1 cause of your Q. Push Lane to become level 2 earlier. After heading level 2, instantly jump on your enemy with your W and use AA and Q.

First Blood is yours in any case.

Ganks by Jungler

If enemy jungler is ganking, dont be afraid, just kill him. If the enemy team has a squishy jungler, just kill him. Your enemy laner will be low any time cause you poke him with your Q. If you are lucky, you can kill them both.

After Level 6

After heading level 6, go back and buy. Jump on botlane your midlane to get one more kill and to give your teammates advantages. As Pantheon you can carry 2 lanes.

Advantages

As Pantheon, you can kill any squishy champion. Enemys Adc cant handle a fed Pantheon. You will be fed in any case. Position your E to hit every enemy champion for maximum dmg output.
On lane, you are always stronger cause of your block. You can kill every Toplaner who deals dmg with autoattacks like Irelia, Jax. Champions like this just have no chance. Try to fight all the time, never run. Pantheon is one of the most aggressive champs in the game, your best defense and disengange is using your skills and fight. When you have to lasthit with your Q, you have already lost the lane. Use your ult to come into the range of their adc, you dont have to hit your enemys with your ult so position your ult to just get to their carrys.

Disadvantages

Try to avoid tanks. As Pantheon, you have no chance vs tanks. Try not to fight vs tanks. The longer the game lasts, the more less will be your chances to win the game. Pantheon is really early and mid game, dont troll, try to finish the game as early as possible.