Can anybody give some pointers on killing a rathian. Armor/weapons?

Rathalos armour or anything fire resistant

If you have one a water weapon is great if not then something that has I high attack and if posible a useful atrib like stun, water, poisin or maybe thunder

Yup

Firstly weapon. Anything that has an thunder element on it. I like the SnS Thundertip (made from hunters dagger -> thunderbane)

Armour, fire resistant, i'm guessing armour values of about 15-20 on each piece.

Right, now moves:

Charging: when it charges move out the way, and try to attack it when it falls over. Try to always have a wall to your back, so when it falls over after charging you can reach it, to get a couple of combos in.

Roar: usually signals she is going into rage mode, but sometimes doesn't. Render you helpless for a couple of seconds, can be very annoying. Try to block as soon as you can.

Rage mode: attack, speed up. Watch out for it. Can be dangerous. Either wait until she calms doen, or attack her as normal if you are running out of time.

Throws fireball: this is the best time to be attacking her. Run to the side of her and hack at her legs. I like to take the Rathians tail off first, because it can get annoying. When she throws the fireball, run behind has and slice at her tail 'till it come off

Swings tail round: one of the main reasons I like to chops a rathians tail off, annoying. You can hack at her legs at this point, but just watch out for the tail.

Bites towards left leg: attack her right leg, simple

Scrapes foot on floor: watch for the tail, it will knock you over, even though it doesn't look like it is doing much. You come from the side and hack at her legs if you want.

Randomly looks around: perfect time to hack and slash at her, you will usually get 3 or 4 combos in here, so watch for it.

Flys backwards: Most people block here, but I take a chance and slash at her wing. It has the chance of knocking her onto the ground. There is no danger here even though you are effected by the wind press. This is because you have already recovered before she has landed again.

Items:

Take with you:

Flash bombs: (flash bug and bomb material)

Pitfall traps: (net and trap tool (Net: spider web and ivy))

Small and large barrel bombs: blow them up on her when she is stuck in the pitfall trap.

That is all I can think of for now (as if you havn't get enough there xP )