There are plenty of good tips here on the website, read them all! In addition, talk to people who have already successfully submitted works if you know anyone who has. Once you feel the submission is done, take an extra look at it, just to make sure it’s as you want it to be. If you have the time, let it wait for ca 24 hours before scrutinising again – anything missing? – and then send it!
Since I’m interested in text, I would recommend thinking through the text accompanying your submission; consider the text as an important part of your submission. I am interested in conceptual work where text is often an integral part of the work. The text doesn’t need to be long, it doesn’t need to be clever – but it does need to be concise and well thought through (and do get rid of spelling mistakes by using spell-check). Consider having someone looking it over to test how the text and the submission as a whole is understood by someone who doesn’t have the same insight into the work as you have. And lastly, however stressful a submission can be, enjoy it all and have fun!