Anybody got any tips for 800 metres race?

I've soon got an athletics match, and our normal 800metre runner is out ill and our normal reserve can't make it so I have to jump in and take one for the team. I'm generally pretty terrible, my pb is 2.47 and my recent practices weren't far off, but I can't seem to beat it. Have you got any crucial tips that will help me maybe not come last or at least beat my pb? thanks :)