I tried to make my first Belgian tripel recently. While it tastes like crap, I learned a lot during the process, and I figured I'd share my discoveries.
1) Do not prepare a yeast starter in the primary fermentation vessel. I thought I was being smart by making my yeast starter in the carboy I was going to do my primary fermentation in to save myself the trouble of transferrig the starter. The CO2 produced by the starter culture, however, effectively eliminated the oxygenation of my wort when I poured it into the carboy. End result: poor yeast growth, slow fermentation, terribly over-phenolic taste.
2) Do not add spices to carbonated beer. After kegging (and carbonating) my beer and deciding that it didn't taste right, I tried to fix it by adding some spices that I thought should have been added. I sterilized some spices in vodka then dumped the shot of spices into the beer. The addition of spices or solutes creates a release of CO2 which is difficult to imagine on a 5 gallon scale. Don't repeat my mistake unless you have the irresistable urge to hose your house down with beer.
3) Do not buy clone kits. The recipe I followed was a kit and I knew when it arrived that ingredients were missing. I figured that whoever came up with the recipe must have known something I didn't. The recipe didn't taste remotely close. In hindsight, I should have done some searching for a recipe online before I blindly bought a clone kit that didn't list the ingredients.
Hopefully, all of this will help someone out there avoid repeating my stupid mistakes.