Russian strategy

i formed russian empire and it is around 1690 now at tech 23, i have around 300k men and army composition that fill up the combat width. i have a below average to mediocre economy. granted, i am new at this game so im surprised i made it this far, but i ran into an issue where i let the polish and ottomans get too strong, with strong allies. the polish and her allies outnumbering me massively and the ottomans matching me in numbers but have better army quality. i want to expand into europe without being stomped by polish and ottomans and i saw a strategy somewhere that i should let them die in siberia, but how do i do that?