If you added your event last year just change the date, you can just search for it (or use track tab on your account page) and edit it using the edit tab. You don't have to type it all over again, just make the changes you need and save it, The oldest ones will rank higher in Google, so it pays to update it every year instead of creating a new one. All content is reviewed by human editors so it may not be seen by the public right away.
Add a picture of your race. Pictures attract the attention of the viewer. When adding a picture be sure and add a relevant title that describes your race.
You will do best running as training the same distance of the race you want to prepare for. The distance you run in training should be the same as race you are training for. If the race is a 5k you should run that every day. If it is a 10k you could run it every day if you have been running that distance every day, if not you should work up to it by adding from 10% of your distance a week. If it is a longer distance such as a half marathon you should run it at least once a week and maybe 7 miles 2 or 3 times a week and a 5k on the other days.
I have loved the US Race Calendar since I started doing it around 2000. It originally started it as a race calendar for our running club newsletter that I started doing sometime in the 1980's. I then became the webmaster http://www.grrc.net/ and learned web design. My wife Julie is still the newsletter editor and is club secretary and I am still the webmaster (the only one our club has had) I started a list for the race calendar but it got so big that people just wanted local races so I made a separate one for Illinois and one for up to 50 miles away.