Tall man.....Clothes question!!!

Question here for tall lads (or even girls who can offer some advice) on clothes,

Ok i am 6'2.... i would say i am medium build, maybe a small belly, definitely not overweight though, i weigh about 13.5 stone, so normal enough for my height.

Anyway, thing is, i can never get clothes to fit me properly. I am obviously buying wrong sizes or going to the wrong places. Can anyone give me advice what a fella of my build should be buying in terms of sizes and where i can buy?

For example, if i buy a XL shirt to wear on a night out in Jack n Jones for example, the length might be ok, but it is too tight on the arms, neck and around my waist, so i would maybe buy the XXL so it is a bit more loose, however i have to tuck it in then, and it doesnt always look right. I hate wearing tight clothes.

Would love to hear from others in similar situation, where they go, what size they buy etc? Help a man in need......hehe