I fly small aircraft into primary class B airports pretty regularly, so I'll advise a few things, though most of them are common sense. First, it is good that you're going IFR-that will make it easier for the controllers to plan ahead to fit you in. Second, make sure you are very familiar with the airport's procedures if possible. For example, if winds are ___, you assume that runways _____ are in use. This helps with general situational awareness, and is important with the third piece of advice I have: remember that when you're on the ground, the flight is only half over. GA pilots can make themselves pretty dangerous by not knowing where they're taxiing, which brings up this: if you are not sure of something (being cleared to land, what aircraft you're supposed to be following, route of taxi, ANYTHING) please ASK the controller and get it right! Also, be sure you are familiar with wake turbulence avoidance. Other than that, stick to your good IFR habits and it will be fun. As long as you are smart and proffessional, no pilot flying heavier iron or an impatient controller will care how big your destination airport is. I've never had a hard time flying into MCO, it's so spread out and never seems to be overly busy. If you're a little apprehensive that's good, it means you're probably not careless. But after you do this, if you do it right, you'll realize how simple it was and you'll grow as a pilot.