begin game:

if you start on the left side and you must help you're jungler I recommand you play safe and try to get some fury. if you start on the left rigth side you must try to make some profit that you're opponent is helping the jungler and get some fury to make a good start.

note: lower then lvl 6: try to focus on you're farm
higher then lvl 6: you can try to make kills and if you're line is pushed go to the golems ore wolves if thats ok for you're jungler ore gank mid.

there are some problems if you play with tryndamere: the biggest one is you're hp bar you don't have a lot of hp so make sure you have fully stacked you're bloodthirster.
another problem are slows and stuns they migth throw you fast out of teamfigths there are not many solutions to that just keep you're eyes open.

counters: here are several counters + tips

nasus: his ulty gives you low atack speed if he cast his ulty try to escape and come back when its done to kick his but.

taunts: they hold you down not only in laning face but in teamfigths to try to avoid them.

jumps: if you're opponent jumps away in a teamfigth try to lay another focus and wait untill he comes back don't chase and leave you're team mates alone.

most people think tryndamere is weak and do 0 damage.
i am going to be very short in that: they are WRONG
tryndamere is very strong only low on hp. (see solution in problems)
if you see that you're tam lays a bad focus try to get the adc and do some pings.
you can perfectly start a teamfigth but make sure you're team mates are close.
defend the adc but not at all costs. you're first priority is to make sure you do good starting damage then the team can finish it and you leave the teamfigth if you used you're ulty to engage.

late game beware of stuns and slows.
you can play 2 styles: 1. very agrasive and engage with you're ulty
2. you can snipe out the adc ore ap-mid burster
try to keep you're farm high and get them!

gl hf