Scrub all parts thoroughly with soapy hot water and bristle brushes when they return from the machinist, then, dry them off and scrub them again. Assemble the engine on a stand and keep a trash bag over it when you're not working on it. Follow torque vales precisely, remembering that torque is always taken on a moving, lubricated bolt. !
Check everything once, twice, and a third time before proceeding to the next step in engine assembly. A good engine assembly lube is half STP and half 10w40. Put in in a dish detergent squeeze bottle and oil everything more than you think it needs.
If you're installing a higher-lift cam, check pushrod length and the arc the rocker arm describes over the valve stem.
Invest a few bucks in precision tools (dial calipers, mikes, ring compressor, etc.) and learn to use them. Trust no one but yourself and take your time.
I keep a running journal of engine specs as I assermble and engine. That way if, God forbid, you ever have to tear it down again, you'll know exactly what is wearing and how much.
Good luck. Patience is a virtue.
1999 SLE K engine