How to say" you gonna do a great job " or "you can do it" ? ( i need a fast answer TT)
I know 화이팅 or 아자아자 화이팅 and 힘내세요.
I want to say literally you gonna do a great job as to cheer someone up, does 잘 할 거야 count?

and how to say " don't be nervous" and " act yourself "? when I want to give someone advice ~
thank u ~

Question

How to say" you gonna do a great job " or "you can do it" ? ( i need a fast answer TT)
I know 화이팅 or 아자아자 화이팅 and 힘내세요. 
I want to say literally you gonna do a great job as to cheer someone up, does 잘 할 거야 count?

and how to say " don't be nervous" and " act yourself "? when I want to give someone advice ~ 
thank u ~

Answer

"잘할거야" works fine.

1) 잘해낼거야
2) 성공할거야

긴장 하지말고, = "don't get nervous, and..."
(너에 게) 자연스러운행동 해 ! = act what in a way that is natural to you

Answer

Yes, you can use "잘 할 거야" and its variants.

Using polite style,
- You're gonna do a great job / You can do it => 잘 할 거예요 / 잘 될 거예요 / 잘할 수 있을 거예요.
- Don't be nervous => (너무) 긴장하지 마세요 / 긴장을 풀어요.
- Act yourself => 평소처럼 해요 (Do as you usually do) / 자기 (있는) 그대로를 보여 줘요 (Show your true self).

Answer

Don't worry. You will do a great job. There's no need to be nervous.  Just be yourself and cheer up!

Answer

항상 너답게 ! = like yourself, always