1999 stuff: Best Vigor is Possession. It is the only vigor worth upgrading. Use it on Patriots and they'll often turn around so you can hit their rear weak point. Use it on high health enemy Flak and Rocket infantry to make them kill themselves quickly. Use it on just about anything to distract enemies while you pick them off. Next best Vigor is Crows because it is one of the only things that hinders Handymen. Shock Jockey is useful for stunning crowmen and firemen. Undertow is useful if you can knock bigger enemies off ledges or ships.
Best weapons are the hard hitting ones like Hand Cannon, Carbine, and Sniper Rifle. With +damage gear equipped you can kill regular infantry with a single Hand Cannon headshot. I only upgraded the Hand Cannon and Carbine as the sniper rifle is harder to use in closed spaces. No need to waste salts on weak infantry when you can one shot them in the head.
The best piece of gear I found was +50% damage on critical hits. Another useful gear I found was 60% chance to stun with melee. If enemies get up close start whacking them and they'll be far less likely to hit back.
Max out your health first, then your shields.
Always find someplace well guarded to hide. Almost every fight in the game can be won by camping a good corner or chokepoint and waiting patiently while peeking out when your shields are up. You can usually run away from a fight, hit up a vending machine, and come back in better shape. You can use vending machines during combat too, if you need a quick heal or ammo.
Don't be afraid of dying once or twice during some of the longer fights in the game. if you've been exploring everywhere you should have thousands of coins with little to spend them on. A few deaths over the course of the game won't put much but a dent in your total. 1999 mode is rather easy with the right strats, weapons, and gear.
ok ok this is getting too much for me. probably the highest yield for lowest effort trolling I've ever done though, besides maybe Fresh Prince.
Figures you wouldn't learn anything from that link and instead keep looking for excuses. I was just trolling guyz, srsly! Yeah, no.