Beginners
I've noticed that beginners play with no tactics. They can be 10th level characters with many magical items and still get slaughtered.
I know my players are like that, although most have played D&D for 6 or 7 years. So when I decided to run City of the Spider Queen, I allowed them to make characters who had too many magical items. I winced when I saw their final character sheets. The wizard of the party had an Intelligence score boosted to 26 and the cleric had 24 of Wisdom. The fighter has an AC of 26! Bear in mind that they play 8th level drow characters. In addition I gave them all Drow House Insigna's, Piwafwis and exotic weapon proficiency(handcrossbow). They have SR 19 for crying out loud!
First game, they barge into the Dordrien crypts and kick major ass. I was starting to regret being pre-game Monty Haul DM. Second game came along, and for those who are familiar with the module, after they killed most of the sentries, I sent the Hunter-Killer team. This group of drow are sent to kill the PCs if they appear really strong. I admit they are strong but I'd say they are equivalent in level to the PCs. In fact, they have less magic then the PCs.
I nearly slaughtered them all. A flamestrike finished the cleric who had 70 hp, the wizard who has 45 hp(yes that much) was in the single digits. The rogue was too weak to help. Only the fighter remained. BTW, I calculated the cleric's odds of getting 70 hp, the player had 1 chance out of about 2 million. I am not saying he cheated or anything... Anyways, it just goes to prove that overconfidence can be the PC's bane.
I don't know any sites that give any advice to PCs, since most games depend heavily of the DMs style. Moreover, those sites would a metagamer's heaven. I like the not so subtle hinting during combat. Just mention either in the description that there's a cliff and bullrushing opponents of it could be nice.