I agree with iceui2. The science buddies guide is good (though not comprehensive in any respect).
Also, you can try intelliprep1.com for science competitions (a really cool private “tutoring” service that has past winners edit your abstract, fix up your paper, and hone your presentation). I won 1st place category at ISEF, and then used them for Siemens also (regional finalist), so it worked pretty well lol. extremely high prices tho… but definitely worth it