The quality of your work can make or break a second order. Don't expect a new client (or even an existing one) to continue ordering from you if your content doesn't make the grade. Over the years, I have learned that doing certain things at the last minute before I send in the work can be very helpful.
Proofread one last time. Always, always proofread again right before you turn in your writing project. Even if you have proofread several times, one more time before submitting is essential. Sometimes that one last time at the very last minute can catch those minor issues you missed before, like spelling "too" as "to" or misspelling someone's name.
Is your content web-friendly? Print writing and web writing are very different. Hopefully, if you are writing for the web, you are aware of this. Beware of run-on sentences, unnecessary modifiers, and other things that can clutter web content. Web writing should be clear and concise. It should also be optimized for search, as well as eye-tracking.
Numbers count. On the web, there is a such thing as too lengthy. How many words did your client request? Did you stick to that plan? If you went over, you need to shorten it up. Don't forget to proofread and count your words again if you revise. In fact, you should still do another word count even if you didn't revise. Did your client recommend a length that you feel is not appropriate for the intended purpose? If it's at the last minute that you made this revelation, submit the content as requested. Include a note with a promise to revise if they wish.