Try doing: verb + thử (coi / xem)

Thử means "try", in the sense of "try it and see". It usually goes after the verb: ăn thử (taste), mặc thử (try on), làm thử (have a go): Ngon lắm, anh ăn thử đi. It's really good, try some.

In Saigon you'll often hear coi at the end, meaning "and see": Chị mặc thử coi. Try it on and see. In Hà Nội it's xem: mặc thử xem. Coi also works without thử: Đoán coi! Guess! And thử can go before the verb, with coi at the end: Thử hỏi anh Minh coi. Try asking Minh.

In a clothes shop, ask Em mặc thử cái này được không chị? Can I try this on?

Thử isn't "try hard, make an effort". For that, use cố or cố gắng: Em sẽ cố gắng. I'll do my best.