Basics

100% Gold, Baby

If you can manage to get 100% completion, you'll receive speeders in the Portland waters and a Rhino at Fort Staunton. In order to complete the game at 100%, you will have to do the following...

Finish all of the missions and side-missions (all covered in the Missions section)
Finish all races with gold medals (all covered in the Missions section)
Collect all 100 Hidden Packages (all covered in the Hidden Packages section)
Complete all 20 Rampages (all covered in the Rampages section)
Complete all 26 Unique Stunt Jumps (all covered in the Unique Stunt Jumps section)

Markers

Reading your markers is vital to everything imaginable in Grand Theft Auto series. You can highlight your map and place a singular marker on it after zooming in. If you're looking to outrun the cops by traveling to a specific destination, just bust out your map and read it over to tell where you're supposed to go. This also works if you find a Rampage or something of the sort while doing a mission, and need to come back to it later. Just place your markers and do your thang.

Ammu-Nation

Everybody's favorite gun shop is back in Liberty City Stories, and they're there for you whenever you might need a little additional help disposing of some pests. Purchasing a piece isn't as simple as it looks, as you will need some serious dough to acquire such weaponry. It's almost easier to just collect the 100 Hidden Packages than deal with spending your hard-stolen money on hardware to blast fools with.

Get Good or Die Tryin'

If you die, you'll be taken to a hospital. You will lose all of your weapons that you had upon dying (hence why it's noteworthy to save very frequently), and if you died during a mission, you'll have a taxi awaiting your hospital exit that will automatically take you to the mission dealer. How convenient!

Breakin' The Law

There are a few ways to lose the fuzz, the bronze 5-0, the poh-poh, you name it... The most obvious or which is getting your vehicle sprayed at the Pay 'N Spray. This will cost you a little bit of cash money, but it's worth it to lose the police. You cannot commit any crimes immediately afterwards or else you will catch the attention of the good guys once again. Another great way to lose the coppers is to run over and thus collect Bribes. Police Bribes are circular icons that look like police badges, and they will reduce your star total by one per icon. While being chased, be careful not to run over tire traps that will rip your rubber to shreds, hampering your top speed and control significantly.