I'm up in early June, so I have the same stuff on my mind. Keep in mind that the fees are increasing from £1000 to £1500 at the beginning of April, so make sure you have enough money saved.
Have you downloaded the guidance along with the application? That will provide a lot more detail. It doesn't seem all that different from the application process three years ago. The main thing is to have the documentation in place--proper payslips and bank statements for salary confirmation, plus documentation for your maintenance payment. The big difference is that you'll have to register for a Biometric Residence Permit. The UKBA will send you a letter a couple weeks after you send in your application inviting you to register your details (picture and fingerprints, I think?) at either a PEO or Post Office (has to be the PEO if you've got dependents). Apparently PEO appointments are quite difficult to get.
Tier 1 applications seem to be taking about 60 days to process right now, so keep that in mind with any travel plans you may have. There's a really useful website here where people keep track of how long their applications have been under consideration, etc:
http://www.trackitt.com/uk-immigration-trackers/tier-1-general-extensionGood luck! There seem to be a few of us right now with Tier 1 renewals