It seems like for some verbs (正)在 is used to indicate action in progress, but I have also encountered 着 for some, like 穿着. When should it be used, is there a rule to follow?
This is used for both actions in progress and things that are happening in present tense, such as "she is wearing a dress".
I sometimes equate this to the -ing suffix.
He (She) is wearing a suit and playing guitar
Help me look out for him (her) (at this moment)
See him carrying such a big thing
However, this is not used as -ing with actions as you would expect:
This is wrong:
The 着 here should be applied to the 游 i.e.
Indicating action in progress.
As shown by @xiaohouzi79's answer.
Accompanying another major action.
As shown by @trideceth12's answer.
Sometimes, neither of the above two can tell the whole story. For example,
走着瞧 (zǒu zhe qiáo) which roughly means Let's wait and see.
你看着办吧 (nǐ kàn zhe bàn ba) which roughly means It's up to you.
You can say it falls to case 1 in some sense. But I feel it's used as a whole, like an idiom.