inversion

"do you", but I would not use a comma here.

(In fact, the version with "you" is possible in colloquial speech, when "only" can mean "except", but I think this is very unlikely to be what you intend.)

Mr WordyIn fact, the version with "you" is possible in colloquial speech, when "only" can mean "except",

Mr Wordy, could you give an example of the above?

Thanks.

A: Am I doing this right?

B: Yeah ... kind of ... only after you start up the generator you plug in your extension cord.

(i.e. he did it right except that he forgot to plug in the extension cord)

Thanks, Mr. Wordy.

You can also use the imperative as an instruction:

Only after you start up the generator, plug in THE extension cord.

MH, what's the difference between your and my "do you" version in terms of mood?

Marius HancuOnly after you start up the generator, plug in THE extension cord.

Hmmm. This doesn't sound natural to my ears.