Here's a few things you can do to make playing your PS3 a more immersive experience.
First off let's start with your PS3's memory. If you're looking to get the most out of your PS3 your going to want to install games, save music and movies and the like. To do this you'll need some HDD space, I recommend buying cheaper PS3's even possibly from Ebay or used then upgrading the HDD.
You can do this fairly easily, go to any website or store that sells 2.5 inch SATA notebook hard drives. And by following this simple tutorial: YouTube - PS3 Hard Drive Upgrade Tutorial you can turn your 20GB PS3 you bought for $250 into a 500GB for an additional $100. Depending where you buy from.
Next, display settings. Often your PS3 won't be tuned for the best output when you first get it, changing these few things can improve display and frame rate.
-BD/DVD: Off
-HDMI 24fps: Off
-PS/PS2 Upscale: Off
-PS/PS2 Smoother: Off
-RGB: Full
-Superwhite: On
Turning off automatic notices can also improve framerate
Playing your games correctly is a big part of this. Some games have the option to unlock the frame rate, this will make the game feel and play a lot smoother and realistic.
Customizing your XMB can give your PS3 a personal feel to it. Apart from the standard themes the PS store offers and the Wallpapers you download, you can make your own Wallpapers with Photoshop [If your proficient with it] upload them online and download on your PS3. Doing this I've made some pretty great wallpapers. Using a theme creator you can further customize your PS3. More info. can be found here.
Having additional hardware can really be an asset. Owning a headset and Wireless keyboard makes gaming more fun, and online browsing much easier. You can buy attachments that add a keyboard right onto the controller if you wish. Or Wireless USB keyboards are pretty cheap. If your TV supports HDMI I strongly urge you to go out and buy one. They can be expensive, but the difference between 720p and 1080p is outstanding. Make sure to check if your TV supports it first, however.
That's all I got for now, I'll add more as they come, feel free to post them.