I haven’t spent enough actual time in Far Cry 2 to call myself any kind of expert on it. Still, from my one play through of the game and miscellaneous advice I’ve gleaned from various forums, here are some tips that someone playing for the first time might find useful:

• Buying a weapon provides an infinite supply of that weapon from any armoury. Also inside the armoury and each safe house are storage cases for each of the three weapons slots. Whatever weapon you put into a storage case will stay there regardless of where you access the case from. This allows you to arm yourself with a particular weapon while travelling to a mission location and then switch to another weapon at a nearby safe house once you get close to actually do the mission. You do have to purchase the cases as separate upgrades before you can use them.
• Buying the vehicle upgrades increases the damage it can take while you’re driving it and greatly reduces the time it takes to repair it.
• Stealth is a completely viable option, especially once you’ve purchased the camouflage suit upgrade. Do note that contrary to what you might expect, sneaking up to an enemy from behind and killing him with the machete is not stealthy because he will invariably cry out before he dies. You need to use a silenced weapon to headshot the enemy for him to die silently. Also note that if you leave the body when other enemies can see it, they will raise the alarm, ruining the stealth option.

• Probably the best stealth weapon is the dart rifle. It kills silently, has a long range scope and kills instantly regardless of which body part you hit because it’s toxin-based. It’s also arguably the best sniper weapon for this reason. It’s disadvantage is that it’s single shot, requiring you to rechamber a new round after shooting and it’s ridiculously fragile, blowing up in your hands only after around 10 shots even after purchasing the reliability upgrade for it, which is a must have if you intend to use this weapon at all.
• Other than the aforementioned dart rifle which goes into the special weapons slot, there are three regular sniper rifles which go into the primary weapons slot. The Springfield is a bolt-action rifle, which like the dart rifle needs to be reloaded after every shot. It’s very cool to use however and forces you to think about every shot you take. Both the Dragunov and the AS-50 are semi-automatic with the latter being also an anti-material rifle so it does good damage against vehicles. Since it’s not really worth destroying the vehicles when you can just kill the drivers, I feel that the AS-50 isn’t really worth buying.

• The most expensive assault rifle in the game is the AR-16. Before purchasing it, be aware that while all of the other assault rifles have iron sights, this one actually has a scope, meaning that it can fill the role of a sniper rifle in a pinch, but this also makes this less than stellar for close to medium range combat when shooting from the hip isn’t accurate enough and shooting through the scope is next to impossible because the enemies are so close.
• Shotguns are surprisingly effective weapons in Far Cry 2 even at medium ranges. This is particularly true in tightly confined spaces, like close clusters of shacks where you can shoot through the thin zinc sheets to hit enemies. My weapon of choice in the primary slot at the end of the game was the USAS-12, which is almost guarantees one-hit kills on close-medium ranges when properly used.
• If you’re wondering what good purchasing the flare gun does, here’s one word: fire. You can set the grass on fire and watch it spread all over the enemies’ camp. The flamethrower can start fires too of course, but it’s very, very short-ranged. Using the flare gun lets you start fires in strategic spots, potentially allowing you to force your enemies to stay within a specific area. Their reactions when they try to avoid a spreading fire is hilarious as well.
• A buddy marked as “Rescue Ready” will automatically show up to haul your bacon out of the fire if you’re going to die. However, once they do that they lose the “Rescue Ready” status. To restore that, you need to sleep at any safe house. When you wake up your buddy will appear at the safe house and you can talk to him or her to regain that status.
• Most main story missions allow you to subvert the mission by performing additional objectives given by a buddy. Successfully completing the missions in this way unlocks upgrades at all your safe houses, providing them with ammunition stores, medical supplies and vehicles etc. However, you lose all of these upgrades when you move from the northern map to the southern map and need to unlock them all over again.
• If you hate constantly being harassed by enemies while driving around, try turning off your vehicle’s headlights. You can still see perfectly well but your enemies apparently can’t see you in the dark until you’re right in their face. In general, doing missions at night is much easier than doing them in the daytime for this reason.
• Alternatively if you also want to avoid fighting the same checkpoint battles over and over again, consider going off-road where possible to dodge the roadblocks or travelling on a boat along the rivers whenever possible. Again, this works better at night because you can go up much closer to them without them being able to see you.
• Finally, some areas to pick up diamond cases are inaccessible without a hang glider. If your GPS beeps about a diamond case being nearby but you can’t find a way to get to it, look around for a hang glider to fly to that location. I didn’t really do much of this however as I hated this part of the game.

Hopefully this will be useful to somebody somewhere.