The three Russian spelling rules

Seven-letter spelling rule:
After г, к, х, and ж, ч, ш, щ — never write ы, instead use и.
Five-letter spelling rule:
After ж, ч, ш, щ, and ц — never write an unstressed о, instead use е.
Eight-letter spelling rule:
After ж, ч, ш, щ, ц, and г, к, х, — never write я or ю, instead use а and у.