first, phreddiva's valentine's lists - in book form (including the as yet unseen 2009 list):
and this post is genius - it puts a lot of things i know in simple terms
i think the one hit home for me the most is
"You can't expect to have what you want if you don't ask for what you want."
this is especially true for me as i've given up on monogamy, so asking for what i want and being honest about what i can and can't give someone is an absolute must (otoh, the asking - damn that can be hard especially when you're shy)
but asking for what you want telling your partner what you need in some way is extremely important
in the past when it has stressed me out/made me too uncomfortable to discuss something face-to-face as a starting point i've used letters or online messages or pointed them at links saying this please - once the conversation is started it's easier to keep talking
and while i'm bi and non-monagamous, the topics addressed apply to any relationship you have - seriously