I don't know why people keep saying to use WW first... you use Bloodthirst first always.
BT - WW - Open - BT - Open - Open - BT - repeat
Open spaces are used for slams and if you have no slam procs during the "open - open" section you stance dance, rend and you have enough time to be back before BT is even up. If you don't have slams and you don't feel like rending, these are the spaces you should be putting sunder armor up.
As for after 20% you don't replace heroic strike with execute, you replace slam with execute. After 20%, no more slams - this is a bit of a toss up if you have 4pt10.
As for stance dancing with rend there are a few macros you can search and use, but tieing battle stance to up on your mouse and berserker to down on your mouse is probably the most effective way to do it, macros can get you stuckin certain stances.
After spending hours and hours raiding, sitting on a dummy and scouring EJ for information - I put together a small quick and fast guide that my guildies can reference to
Check it out if you wish, it has basics that one needs to know for their fury warrior :]
Other than that, it just takes lot of practice, good luck.