When I put my engine together I dunked the pistons top-first into 30W oil and worked it into the rings one at a time. I used tons of assembly lube putting the rods/crank together.

One important thing to remember when youre building an engine is, when it's ready to be started, crank the engine over for about 30 seconds with the spark plugs out. This primes the oil pump and gets the oil up into all the passages. Makes that first start up much more gentle.