AoA has it right - don't forget the big picture. Too many guys concentrate far too much on the instruments inside the cockpit and consequently don't look outside it. GT touched on knowing headings for downwind/ crosswind etc. and that is a good start but in addition it's also a good idea to pick a ground feature to
track towards and that will give you a clue as to how the wind is affecting you around the circuit.
An old flying instructor of mine said that "the earlier you get your **** in a sock the better your circuit will be" so a good landing is a result of a good approach, a good approach is a result of a good base leg, etc. etc. (Not that I'm used to base legs - oval circuits are much easier!!
)
The trim of the aircraft is also vital during any circuit. If you consider that there are several configuration changes (or can be) and speed/attitude changes, then your trim
has to changein order to take these changes into account. Believe me when I say that it's far easier to fly an aircraft in trim than one out of trim!!
Hope this helps a little.