Assuming its the BB area, chainring bolts tight and it's not the seatpost.
All BB's should all be installed with copper slip or similar, grease will work and the thicker the better as it will stay in there for longer.
In the case of an external BB, most come with rubbish plastic spacers. Over time / repeated fitting / over tightening etc these deform a wee bit.
This allows the BB cups to move around a tiny bit and especially when the threads are 'dry' due to no grease or the grease working it's self out of there is often the cause of creaking.
I found it to be at its worst on my Ti frame.
Its possible to get hold of alu spacers which will not deform so readily and teamed with copper slip will solve the problem (it may return periodically but mine dosn't), chris king bb's come with these but a bike shop found some lurking in the workshop for me and gave them to me for cake.
Also, assuming external BB type
Frame should be faced
BB cups should be tight into the frame
Cranks tightend into place with the plastic doofer by hand only
pinch bolts nipped up bit by bit together and equally.