circuit (traf.pattern)in the 320?
 

what altitude do you use to enter in downwind?

do you use the wingtip as visual reference?
what about the 321?

better way than the FCOM?

We don't really fly circuits as such on the line. Perhaps you are referring to base training though? In that case the TRE will no doubt have organised a plan with ATC taking into account the local terrain, traffic etc. When we did it it was more a case of turn upwind at around 1,000ft or so then pretty much a continuous shallow turn onto downwind levelling off around 2,000ft from what I can remember and using your ND you wanted to be about 5nm abeam the field on downwind to give yourself some "space" to be able to turn in on base and finals. All this was done with the bird which is a great tool to help you fly straight and level. Base training is all about using your mark 1 eyeball in anycase so the only thing we had were the papis to get us back to terra firma.

You can't see the wingtips without breaking your neck so we don't bother using those as a reference. The ND is your best tool plus any ILS/DME/VOR that may be tuned in to give you a fighting chance. The PROG page with the runway threshold in it is also invaluable for bearing and distance.

Now if your talking about a quick return to land after say an engine fire on take off then just follow the FCOM. Thats what we do in the sim and it works out fine.