Some missions allow you to pick your aircraft, but your selection doesn't affect your score. Start with capable aircraft such as the F-15 and F-16 and experiment with the F-4 or the Mirage when you want a challenge.
The documentation isn't very clear on how to start a multiplayer game via Jane's Online. Connect to the Web site, then sign in and follow the IAF buttons to the IAF page. After you select a session, the system will automatically start your copy of IAF on your PC.
Learn to delegate tasks to your wingman. On some missions, it's imperative to your success. Your wingman seems to be a glutton for air-to-air glory, so you'll usually have to handle the ground targets.