Aim of the Game
The game has a rather generous auto-aim mode tucked away in the config' menu in the options screen. Set the targeting mode to casual and you'll have an easier time as your gun has a much more reliable lock-on to enemies. If you want more of a challenge, simply turn it to expert and all auto-aiming will be off.
You'll kill a ton of bad guys as you make your way through the game, don't forget to run over their corpses to not only refill your ammo count, but by pressing Y/Triangle , you'll also loot their bodies for some easy money. You may not get much cash, but it all adds up!
Whilst the game has the ability to save automatically, it's wise having at least 2 separate saves on the go at any one time. This means you can have two separate games on the go at once, one for being good in, and one for being bad in.
Dead Red Eye
Your Dead Eye allows you to slow time down to line up multiple shots. It's basic at the start, but the number of targets you can mark increase as you go through the game. You need to kill more enemies to refill it, or buy appropriate bottles at the general store to top it all up in one go.
Keep an eye on the brightness of your weapons recital, as the whiter it is, the more accurate your shot will be as this indicates that the enemy in your sights is within range of that particular weapon! If it starts to fade, then you're too far away.
You can purchase a rather useful piece of garment from either the tailor in Thieves Landing or the General Store in Escalera (Mexico), the Bandana allows you to commit crimes without affecting your Honour rating!
Common sense this, but as you can take cover behind most inanimate objects, doing so in a battle can save your life. However, make sure the cover is suitable, as a low wall can still get you killed by enemies on higher ground.
As long as your head is covered you can either pop out of cover, or simply hold fire to do a 'blind shot' into the general area of your enemies (with much less accuracy).