In terms of ingredients and combinations, here are a few things to keep in mind:

1. Only one fish portion per package — think about 6 ounces. Any kind of fish will work, but use skinless fillets if you can, because the fish skin will get soggy when steamed.

2. On top of the fish, you can pile herbs, vegetables, citrus, garlic, and of course butter never hurts. Just don't put anything inside your parcel that won't cook in 15 minutes. If you insist on doing so (like, say, you REALLY love potatoes), cook them almost all the way through BEFOREHAND, then finish them in the parchment with your fish. And use common sense — if you want to include carrots, they should be cut into matchsticks so they cook very quickly.

3. After that, you'll need a couple spoonfuls of some kind of liquid to steam the fish. You can use water, but using wine, soy sauce, citrus juice, or something else with a strong flavor will make your fish especially delicious.

4. Never underestimate the power of salt and pepper.