Yes, call her pretty, or even better.. call her beautiful. But if you REALLY want to compliment her, use words like: hot, sexy, steamy, stunning, naughty, glorious, and even delicious. They will go a long way to making her feel like she's really got your attention and can hold onto it.
A sentence like this will always be well received, in any situation: "Sweetheart, can you help me with this, you're really great with figuring out things like this, you're so smart..."
Find her most amazing attribute and compliment the heck out of it. Whether she believes you or not, you are doing wonders for her self esteem and ego by letting her know she's special in some way. For example: "Holy smokes, lady.. every time I look into your eyes I just get lost in them... *sigh*..." Steer clear of boob and butt compliments. We know they're likely not sincere and they come from your "little head", not your big one.
If she mothers a child or children, make sure she knows how much you value that and how good at it she is, especially when she's having a "bad parenting" day and is feeling low. It can sound something like this: "My dearest one, you handled the permanent felt marker on the wall better than most parents would have. Why don't you take a small break while I figure out how to wash it off... there there.. don't pull out any more of your hair, your hair is so silky and glorious..."
Here's a simple one: "Babe, you make the most superb roast... thank you for cooking, tomorrow it's my turn!" She needs to feel appreciated in all the things she does or she's likely to just think you take her for granted and will stop doing them. Imagine if women stopped doing? *shudder*
Wana know the kicker? All of these can and should be reversed and used for women to compliment men with too! Equality in partnership. It goes a looooong way.
Have fun complimenting!