You can use whatever topic you want, as long as you remember the following:
Do not overload your pizza, and wet toppings, like slices of tomato or pineapple, have the risk of making the bottom soggy. That is no problem, but it is nicer to have it dry and crisp.
When you use tiny tomatoes, cut them in half and place them on the pizza with the sliced side up, to prevent leaking. I use San Marzano tomatoes because they are both sweet and a tiny bit bitter.
Cheese, cheese, cheese –I will be the first to agree, but too much cheese (and especially the fat from the cheese) will also soggify the pizza crust. Moderation is key. Buffalo mozzarella is nice, but is wetter.
It is your pizza. If you like specific combinations, knock yourself out. The classics are classics for a reason, but I am not scared of experimenting. I never had a pizza with sweet onion and dark chocolate and I am curious how it tastes. Pineapples (the dreaded Pizza Hawaii) is no pizza according to the Italians, but it is popular for a reason: it tastes sweet, and nice. If you feel like it, don’t let conventions stop you.
Be careful with the amount of anchovies. It has a stronger taste and is far saltier than you would guess from the size.
You bake the pizza very hot, and also very short. Slice and cut ingredients in small pieces to ensure they all cook through and through. Be careful with larger pieces of fish and meat (chicken!). Precook to be sure.