In a noted departure from previous Final Fantasy games, Final Fantasy XV has done away with turn-based combat. Instead you're going for speed and style, with one button each for attack and dodge and the rest kind of up to your movement – attacks are modified by the thumbstick, i.e. pointing it up might launch you into an aerial attack. It's easy to learn, but harder to feel like you're actually good at it, so here's a primer on some things that'll help you on your way.
Learn to dodge, block and parry
I would be lying if I said you can't get through some fights by holding attack and hoping, but eventually you're going to have to introduce some defensive manoeuvring (assuming you want to stay alive). Noct's dodging is really effective – he does a kind of side-step magical phase-shift out of reality for a second – and because the combat is so fast paced you won't necessarily lose attacking momentum by getting yourself out of danger.
Likewise learning to time your blocks and parries is invaluable, especially when you're in a boss fight or up against an uncommonly massive monster, because parries can do a helpful amount of damage and give you an opening to press your attack.
Magic is amazing (also dangerous)
Do not go into bat without some kind of spell up your sleeve. I cannot understate how useful a spell can be if you get the right elemental mixture, even against humongous enemies. By adding in different ingredients you can boost the spell with additional abilities. These effects can be amazingly helpful, so experiment. The trade off is that spells do friendly fire damage on you and your buddies, so time when you use them carefully.
Use your team's powers
Part of the screen furniture during a fight is the Tech Bar on the left hand side. When a section of this is filled up you can activate one of your teammates' abilities to do extra damage. Gladio can unleash a huge spinning attack which is great in groups of enemies, Prompto can do pinpoint damage to a single enemy, and Ignis can pinpoint enemy weakspots with his knives.
Spend your Ability Points wisely
You earn AP as you level up and do cool stuff, and then use them to buy new abilities on your Ascension tree. You can use them to increase your active combat and magical abilities, but you should also take a good look at your recovery (which governs things like your HP) and teamwork trees. If you spend points wisely you can buff your team with new attacks, and give them the ability to perform first aid on themselves when they're in a tight spot in a fight. Making your buddies more self sufficient was, I found, key to surviving long-term fights.
Hit the blindside
Your combat is graded on your offense, defense, and stealth, the last of which essentially grades how good you are at flanking enemies. This is something you should strive for because hitting an enemy's blindside does more damage, especially if you dust off a blindside link with one of your pals, as well as keeping you out of danger from the pointy end of whatever you're fighting. It is worth noting that owing to the ridiculousness of some enemies their blind spot isn't always where you'd expect it to be…
Don't be afraid to not lock on
There's a button to lock on an enemy in combat situations, which is more useful in some scenarios than in others. When you're specifically targeting a spell or a warp attack, it's all good, but one of the down points of the game in general is that the combat camera can be a bit of a bastard – a technical term – so if you can learn to wrangle it around yourself you might end up better off.
Update your gear frequently
Generally speaking the further you get from your starting point, and the further along the story you go, the more the enemies are a bunch of hard bastards like giant skeletons with scythes or terrifying armoured wasps with giant stingers, that kind of thing. Given this you can't stick with the standard weapons and accessories you get at the start. As you move further remember to keep checking in with vendors to see if they have weapons that deal higher damage or include elemental buffs, and swap around your accessories when you get new ones to make sure you're getting the right benefit in the right places. It can make a surprising difference in a fight.
Use warp, because warp is great
Warp is a teleport power specific to Noctis. He can use it as a warp attack, which does extra damage and can break enemy attacks, which is great, but it's also amazing when you use it defensively. You can warp in any directly to get out of combat (if, for example, a boss enemy is about to do a massive area of effect attack and you need to get out of the way really quickly), so it's a great flanking manoeuvre, and it can be levelled in a few interesting ways on the Ascension tree. You can also use warp to get to high vantage points during a fight. Doing this gives Noct a bit of a breather to regenerate some health, and it refills your magic instantly, meaning you can get back to warping all over the place. Point-warping is a good way to maintain Noct's speed and agility in combat.