Hi,
I guess "tip" is the most informal and general of the three. if you think of possible uses, you can talk about "tips to get a good tan", "tips to look great" and that kind of magazine stuff ![Smile [:)]](/emoticons/emotion-1.gif)
"suggestion" is closer to "idea, proposition", for instance "going to London was her suggestion"
"advice" is uncountable (you can say "a piece of advice") and it means "to make a recommendation about a certain course of action. it has the connotation of "this is for your own good" (like "counsel"). for example, "a word of advice from a friend will make things easier"
well, I hope it's a bit helpful. best of luck!
Ale