Why on earth we can't learn from the mistakes made last time I don't know. It wasn't that long ago. It saddens me when I hear "but it's different this time" because, no, it really isn't.

Keep with web standards (real web standards, not pseudo-standards from a large corporation) and make sure your stuff works in at least a basic way in all browsers that your users may need (seriously, not everyone can update to even a browser 2 years old, never mind the nightly bleeding edge build, due to company policies, so stop coding for that please).