The first thing I would do, would be to replace the standard Samsung Touchwiz interface with a different launcher. There are several options here, and I can't really speak for all of them, but I've heard that GO Launcher uses the least resources of them all, thus making it very smooth. I've tried it myself and it is indeed smooth and quite cool.
Personally I use LauncherPro, and am really happy with that. Makes my phone seem a lot snappier than if I were to use Touchwiz that comes with the phone.
Other people swear by ADW Launcher EX, which I personally haven't tried yet. (I tried the free version, and while it seems good, I just prefer LauncherPro for some reason, although I believe ADW offers a bit more customization, if that's what you're after)
Then there's also Zeam Launcher, Helix Launcher, PandaHome and I think I saw a Windows Phone 7 style Launcher too. There's probably more than that, but just search the Android Market for "Launcher" and you should find plenty.
As far as battery life is concerned, I don't really know. I use something called Auto Memory Manager. I just started it, set it to aggressive and left it there. It's supposed to close programs in terms of how much memory they use, so not sure it's as effective as a normal task manager, but I've also heard that we're not really supposed to use those? Someone else would have to confirm that, though.
All I can say is that for my own use, it seems that battery life is sufficient, yet I don't have any numbers to show yet. Also it does seem a bit better after using Auto Memory Manager, but I've only had the phone for a few days, so can't give rock solid conclusions here.
As for Applications and Games, all you need is a memory card (the phone comes with a 2GB mem card) and just try to avoid installing too many Apps that can only be stored on the Phone memory. You'll probably want/need SOME of those, but just get the "Apps 2 SD" application from the Market so you can see if you have something that can be moved to your SD card (although my phone seems to always automatically install everything to the SD, which is quite handy
)
So, in conclusion :
1. Replace the standard homescreen with a Launcher from the Market
2. Get some kind of Memory manager or Task manager
(although if you long press the Home button, your phone has its own Task manager, which should probably be sufficient as I've heard that those Auto Task Managers are bad? Some say they're good, some say they're bad, I dunno what to think really)
And that's pretty much it, I'd say.
The rest is pretty much about trying different things and see what works for you, as there are only so many things we can answer for you.
Hope this was helpful in at least some kind of way
