1) So, if you have to check in online- do it as soon as you can. If you forget to print your ticket before arriving at the airport, or if your printer should break down or something like that, it is better to do it as soon as possible. With Ryanair you can check in two weeks before the flight up to two hours before the flight. This time I checked in through the Ryanair app on my phone, so basically I have the boarding pass there, but if there should be any issues with it I preferred printing the ticket any ways, just to make sure nobody will make any fuss at the airport.
Also, make sure you have your passport and tickets ready- if you forget them at home, you're not flying anywhere.
2) The next thing is probably being on time. If you have to check in your luggage, make sure you arrive at the airport two hours before your flight. If you only have hand luggage with you, you don't need to be that early, but somehow I was always there two hours before my flight as it made me worry less.
Don't worry about waiting at the airport- you can go eat something or stroll around the shops, look at planes taking off- all these things are better than being late for your flight.
3) Once you are on time and checked in your luggage, it is time for security. And this can be very stressful, so it is always good to be prepared. Wear comfy clothes, if you wear jewellery, than only pick gold and silver, metal won't let you through the security without taking it off. Shoes, belts and bras can also be a problem- be prepared to quickly take off your shoes, and for women touching your chest area (can be awkward in front of all other passengers). All electrical devices should also be kept in one bag to quickly place them in the trays that go through the x-ray machine. If you have any liquids in your hand luggage, don't forget to put them all into a small plastic bag, that you can also get from the airport, and don't forget that the products can't be bigger than 100ml. If you don't take this seriously, your things will stay at the airport. You will also need to put the liquids through the x-ray, just as your passport and electrical devices, jacket and shoes.
5) On the plane, make sure you store your hand luggage and be prepared to stand up some times until all passengers take their seats and so on. If you are nervous of flying, try to relax, listen to music and read a magazine or a book. I always buy myself one or two magazines at the airport and I always have my iPod and headphones with me, so that I have something to do on the flight. Sleeping is quite uncomfortable, but you can always try it. My flights last usually from 2,5 to 3 hours, which is not too bad, but it is good to organise your time.
6) Once you've landed, don't forget to take all of your belongings from the plane. If you have no checked in luggage, you can go straight to the exit, and a passport control before that and then you are all done and can leave. If you have some more luggage, go and wait for it after the passport control, then you can finally leave. But, remember that there will be tons of luggage, and lots of bags will look the same. Make sure you tie a bow on a handle or make your suitcase recognisable for you.
These are all the tips I can think of just now. I hate it when I am not organised, so I will be following those steps on Monday as well.