Not Updated For Current Season
Passive - This ability has massive synergy with Tryndamere's other abilities and overall play style. The more hurt you are, the higher crit chance you have. Do not confuse this with damage, just because you have a higher % chance, does not mean you are completely more powerful. However, in most cases it does make you have more damage output. While laning, I find that it's ok to stay around 60% hp for a little extra crit. Throw a few auto attacks at enemies while farming, if you get lucky and crit them, you will deal good damage.
Q - This is one of Trynd's most important abilities. Blood Lusts add to Tryndamere's AD, which means his crits will hit harder as well. They can almost be used like lifesteal, crit some minions and last hit them, then press Q to heal yourself. However remember that when you consume your blood lust stacks, you will lose the AD boost.
When I'm hitting a tower, I try to have as many stacks as I can, because you cannot crit turrets, so extra crit chance from being hurt will not help you damage the turret.
In battle, keep in mind that you can heal yourself if you get too hurt. Tryndamere likes being pretty damaged so his passive gives him more crit chance, but being dead is not good. By Q lvl5, you should be able to heal yourself for a good bit of hp with 8 stacks.
Later into the game, you will have more crit chance due to buying crit items, so you will stack blood lusts more frequently. This means you can consume them more often for a quick heal. However keep in mind that the more stacks you have, the harder you will hit.
W - This is a great aoe slow. It makes for good chasing. When your enemy is running from you, use this to slow them significantly. It also will reduce enemy AD, so use this in a team fight to make the enemies less powerful. One nice tip for W is to be looking at it when you get near a bush. If W lights up for use, that means there is an enemy in the bush. This way you can essentially 'face check' a bush, without actually going inside it. You can also detect stealthed champions this way too.
E - This is a great escape/initiating ability. It works like a slower moving flash. You can go through walls too! Whenever you're going to engage an enemy, spin at them to get some extra damage and get up in their face. Every time you crit, the CD will reduce, so if you need to back out, either just spin right out, or go through a wall. This is a nice farming ability too, since it's aoe damage.
R - The ultimate ult. You become fully immune to death for 5 seconds. Sounds amazing right? Well, these 5 seconds will run out sooner than you'd think. Especially if you get CC'ed. CC will be your main enemy while ulting, enemies can easily kite you and hold you down while they wait for your ult to run out. This is why I take Cleanse, Cleanse will remove almost all types of CC from you, and reduce incoming CC by a percentage. Be sure you Cleanse quickly when you get hit with CC so you can make use of your 5 seconds of rage mode. Quicksilver Sash doubles your cleansing abilities, you can skip that item if they are not CCing you too much.
Using this ability as an escape is some times necessary, but it's better to use it offensively than as a defense. Kind of hard to explain. You don't want to use it because you're getting killed and you're not doing any damage back. It's better to use it when you're fighting your enemy, and if you're about to die, use it and continue to kill them.
This goes without saying, but please remember to use your ult before you die. It's not automatic, you have to click it before you die. Remember you gain Blood Lust stacks when you ult, but don't consume them while you're invincible. Take advantage of the extra AD and use the heal at the end of your ult so you don't die instantly, assuming you haven't run to a safe spot.
I take Cleanse so I can avoid CC, which shuts Tryndamere down. Ghost for chase/escape, Exhaust is also a good choice.
I go into offense to improve my crit stats. The rest I throw into defense for a little bit of defensive stats.
I start with Brawler's Gloves for a good start on crit chance, + a hp pot in case I need it. Afterwards build it into an Avarice Blade, so you can get an even better start on crit chance, as well as build up some extra $ too. Next I build Berserker's Greaves for AS, if you're having problems with CC, build Mercury's Treads instead.
Next, I set my sights on an Infinity Edge. This item is extremely important for Tryndamere. Not only does it give good crit chance and damage, it makes your crits hit a lot harder. For a champion that is centered around getting critical hits, it goes without saying this is the most important item to get. I choose to get it early rather than later so I can maximize it's utility. Instead of waiting until way later, which wouldn't be as good because you are sacrificing a ton of extra damage you could be doing if you did have IE. I start it off with Cloak of Agility, if you have enough money, you can get the BF Sword first.
After , I get a Zeal, which gives AS, crit chance and a bit of movement speed. After that, assuming the enemy team realizes how much of a threat you are, they should be CC'ing you as you ult. Cleanse can block one CC and reduce a few more, but it has a decently long CD so it might not be enough. I build a Quicksilver Sash if i'm having CC problems. It gives good MR and another Cleanse as an active ability. However, it can also cleanse suppression, so you can make my poor buddy Malzahar useless against you :/. You MUST utilize the active of this item, if not then it's not worth buying. Be ready to use it if Cleanse is on CD or if you get suppressed.
After that, I get a Vampiric Scepter for lifesteal, which you will later build into a Blood Thirster.
After that nice survival item, I finish my Zeal into a PD. This gives a good amount of AS to balance with your AD and crit chance. It also gives you even more crit chance, enough so that you should pretty much always be critting. The movement speed helps out too.
Next I build a Blood Thirster for great AD and awesome Lifesteal. While you may be thinking, "Why would you want to be healed with Lifesteal if being low on HP gives you more Crit chance?". Well, by this point in the game, you shouldnt need to be very hurt to crit almost all the time, plus your massive damage output will allow lifesteal to recover massive amounts of your HP. You might not even need to ult as much because you will be healing yourself for great amounts.
Lastly, I finish my lonely Avarice Blade into a Youmuu's Ghostblade, which gives more good stats and another active to use in combat. If you want more survival you can get something like Guardian Angel instead.
Marks and quints should lean toward improving your crit stats or armor pen. Seals should help out crit too. Glyphs I get MR, CDR also works. Whatever you like.