There are plenty of teachers who can give you far better advise on this than I can, but a few general hints:
1) Make sure your flute is really warm. (I have been known to leave mine on a radiator for a few minutes in the height of winter before even starting to play) There is no hope of hitting them well if your flute is cold.
2) Remember to blow right across the hole, tilting your flute backwards might help a bit, or try aiming your breath at the back of the hole more.
3) Hold the flute really horizontal, kills your arms, but works wonders for your tone!
4)Think high, this often cures 'can't hit them at all syndrome', so it might help with airy notes too.
5) Try cleaning you flute out. (Also can work sudden miraculous wonders)
6) Upgrade flute (this isn't necessarily a viable option I realise, but when push comes to shove: a silver headed flute is easier to play than a standard student model)
As for exercises, my teacher was a strong advocate of long note practise (play each note for as long as possible, concerntrating on tone and dinamic changes, so start quiet, build up, and end quiet) octave leaps (horrible things, start on, say Eb1, slur to Eb2, slur to Eb3 and back down again) and top end chromatic loops (eg play Eb, E, F, F#, F, E, Eb, is quick, slurred sucession)
Finally, I strongly recommend you do these, at least for the first time, when there is no-one else in the house, and preferably when you neighbours are out. They generally
do not sound anything near decent on the first attempt!
Good luck.