If you flying a 737 with an ND, circle to land is very easy.
Prior to commencing the approach, either enter a 2nm final at 3deg, or put a 2nm fix ring around the RW threshold position.
A 2nm wide downwind works very well. If the ND is on a 10nm scale, the the base of the aircraft symbol (the triangle) is equivalent to 1nm, so estimate twice that width from the runway indication, and you have a 2nm wide downwind. If you have a 2nm fix off the RW threshold, you can also use that to estimate the downwind width.
Fly downwind at flap 5 and 1500'agl, extend gear and flap 15 when abeam the landing threshold if a visual approach, or otherwise gear down flap 15 if as a part of an instrument approach with circling.
Abeam the 2nm final point, extend landing flap, begin base turn and commence descent. Set the same thrust and pitch settings as you would use stabilised on an ILS. Complete landing checklist.
Aim to fly a standard 3deg descent rate (approx 800fpm should work out nicely at most weights). Because your total track miles until landing is approx 5nm (i.e. 2nm base width + 2nm final length + a little bit extra for the turn), descent from 1500 feet at 3 deg will work out perfectly. Adjust descent rate using the 2nm final point as a guide to descent rate, you should aim to fly over it at 600'agl.
If you need a bit more room to make sure you get stabilised, you can easily modify the procedure to a 3nm final, however if you are flying this as a circling approach, the 2nm final procedure makes it much easier to remain within the 4.2nm circling area.