Don't fit bolts without tensioning immediately.
Tighten all series of bolts evenly in a criss-cross pattern, in 2 or 3 stages.
Lubricate all threads and bolt head contact points. Use tension wrench where necessary. (big ends, mains, head, rockers, flywheel, cam gears etc. etc.)
Use locktite where bolts require safety lock. (cam thrust screws, chain adjusters, oil pick up mount, camgear, etc.)
Never fit sump plug without new washer and tightened. (either tighten or leave out, this applies at any stage from dismantling to final assembly) Setting up should involve the placement and counting of every nut, bolt and washer in an order. All parts should be accounted for before any assembly is attempted. The last thing you want to be doing during assembly is wandering around looking for bits and pieces. This will only lead to frustration and the possibility of mistakes will increase.