I hate to be That Guy, but some of you guys need to cut the OP some slack. The difficulty of the missions, especially to new players, is pretty high. I play some "hard" games now and then, and I certainly couldn't win every mission the first (or even fifth) time through. Some people probably can, and that's great! But not everyone can do that.
Let's try keeping this community civil. If you don't agree with the OP, fine. Offer a few suggestions. Point him/her to some useful threads offering tips. Suggest a mod or player-built mission that's not as difficult so he/she can get used to the game at a friendlier pace. Or, if you really don't want to bother offering some help, consider leaving the thread.
Sorry for derailing the topic any further.
The sandbox portion of the game (not too far from release, now!) will give you some control over how difficult the fights are going to be. You can take your time building up a comfortably powerful force, then prey on weaker targets until you get some experience with handling your fleet.
The way I learned to beat the missions was, honestly, a lot of trial and error. A few can be beaten with pure piloting skill, but the others will need careful fleet management. Since the enemy force is often numerically superior, you'll want to deny them objectives as soon as the mission starts. If they get control of too many points, they'll start to steamroll you with sheer numbers. (This is a fun challenge later.)
It's a difficult balance, and some of the missions are very puzzle-like in their solutions. If you want, there are some threads that offer help for specific missions. Sometimes it just takes a change in your initial order of battle.