Well done for your first try! I'd recommend the following things:
- It would be good to give a little more breathing room between the titles and the windows - could afford to go down in text size slightly
- You'll want to smoothen out the curves used to taper the red cheatline up the nose and tail, they're a little disjointed and inconsistent
- Personally, I wouldn't use such a detailed, realistic crown on the tail just relative to the rest of the pretty plain livery, but that's entirely up to the artist's discretion
- Also, perhaps put the "BRITISH AIRLINE GROUP" title located above the aircraft in white text, and change the steel blue background to the same darker blue that's used on the actual fuselage
- Not a huge fan of the blue engines or the white patch on the wing fairing without the cheatline, but again that's totally up to you
Keep designing and you'll find yourself getting better and better :)