Well my advice is get to know the phone on your own a bit for starters, it's closer to a pc OS then any other phone I've ever had and it took me a week or 2 to understand it properly.
As for 'tweaking', the system handles it's memory pool and everything else pretty well.
The only 'tweak' I've made is installing a new homescreen launcher (which is basically just another app: HelixLauncher) which is alot faster and provides some more functionality, but the upcoming update of the OS will fix that anyway.
And I replaced the stock keyboard with the HTC keyboard, for which I created my own skin
For the rest it's loaded up with tons of apps, but you'll have plenty of fun discovering those on your own
(you can use sites like appbrain or androidzoom if the market app feels lacking in search functions)
There are however some tweaks that should help with the relatively short battery life, but those require root.
Flashing your kernel with an undervolted kernel (every action takes up less power). And using setCPU to keep your processor cycles low when idle.
But again, I'd advise you to wait a while before rooting and just read lots of topics here
I myself am waiting for the update of froyo before deciding if I root or not.