This is kind of a common situation. Basically, it's heavily multi-way, very wet board, we're OOP, have a set, concerned about things checking thru and we lead. Here's a specific example but this is a common scenario.

We have 7♦ 7♥ in BB. MP1 raises to $15, 3 calls before it gets to us, we call.

Flop: 8♠ 3♠ 7♣ Pot $75 SB checks, it's on us and we want to bet.

How much and why?