As long as it's ok with your Dr and it is a pressurized cabin (most commercial planes are) than it is usually ok. I flew twice when I was pregnant with my 1st and the only thing I noticed is that during take off and landing the baby kept kicking!!! (I was like 5 1/2 mpnths at the time. Good luck
I've read a fair amount about this, and as long as you have an uncomplicated pregnancy it should be okay until the last two months. If you google it, there is some good information. I just flew back from overseas (I'm just 6 weeks now), but it was like normal except I seriously rested for about 2-3 days after returning. I also have to fly back overseas as I'll be moving there when I'm around 10 weeks.
I would say definitely get an aisle seat so you can get up a lot to use the bathroom (of course!) and so you can walk. The exercise of getting up a lot really helps. If you have any food aversions, ask your airline about some of the other meal options: vegetarian, non-dairy, kosher, etc. These might be more "mellow" foods than the usual chicken or pasta.
The other thing is REALLY allow extra time in the airport. I consider myself a seasoned traveller, and on this first flight being pregnant, I was more nervous making sure I could get to the plane on time, etc. (There was traffic) But I got panicky in a way that I never do, I think because I was really concerned about everything "going right". So do that for sure.
As always ask your doc too! xx