First, when you get the okay to go IC for the first time, and any time thereafter when you type +ic, make sure that you are prepared to do so. Know your character's mood, present emotional state, motivations for what you are about to do. If you are going out, know where you are going and why. Make sure you've got the right clothes on and are in the right place, what were you last doing IC, and why.

When you make your way into the world, and encounter other players, a good thing to do is take advantage of +rwho. It will scan just the people in that room and tell you who is IC and who is not. Sometimes, people forget to set themselves IC, and if you find a room filled with OOC people, you could page them and ask if they are all OOC, or quite often you'll find that they tell you, posing with +sooc.

Sometimes you'll find this entirely un-necessary, as people will pose in response to your IC pose as you enter. When you enter the room, you should pose that you have done so, where you are, what you are doing, and so on. The people already playing in the area should pose their positions and dispositions as well. However, it is very easy in the heat of roleplay for this to get overlooked. Do not take offense, just page or ask OOC for the IC setting. Some times you can help just by posing what you are doing, and who you are doing it in relation to. It never hurts to tell everyone in the room, including the people who are already there, what the situation happens to be at the moment.