The easiest mistake is not balancing the ingredients right. Be it from misreading the recipe, using the wrong type of sugar, or winging it and not using a recipe at all (I am most guilty of this), mistakes with the choosing and measuring of ingredients are very common. Similarly, putting the ingredients into the mix wrong is also very, very common. My most common mistake is not beating eggs before adding; I just chuck them in at the same time as everything else and hope it mixes alright. Also, warm or melted butter/margarine is a must, as cold it will just clump everything together, which is an utter nightmare to whisk by hand!
If you put the mix in an non-greased tin, then there will be serious problems getting it out, often the result being the bottom of the cake being only half-present. A worse mistake, as I discovered yesterday, is coating the tin in tin foil. This makes the oven's rays reflect off of the foil, ruining the middle of the cake top, as you can see below.
Ovens are annoying on their own, with each one operating differently. Add trying to bake a cake into the mechanical mix and disaster is likely. The whole Celsius/Fahrenheit/gas mark issue makes reading the recipe's instruction hard, especially if only one form is specified, as then it's a case of converting and/or guessing. Speaking of which, guessing = BAD. I'm always assuming X temperature is okay, only to discover it's too hot or not hot enough. To make matters worse, fumbling with the temperatures and settings whilst the cake is still baking will result in varied results, from sunken cakes to burnt tops.
|This disaster of an almond and poppyseed cake was caused by guessing the temperature and messing around with the oven settings whilst it was still cooking! EDIT: Also, tin foil is a big no-no.|
The simplest oven mistake, however, is putting the cake too high up. I've lost count how many times I've used the top rack of my oven for the cake, and wondered why the top is blackened and burnt whilst the rest is still raw mix! To avoid, pop it on the bottom rack, or lower the top rack (if possible). Another mistake is opening the oven door when the cake is still baking; this results in a flat or sunken cake. This is worst when the prior mistake is also made, as you're opening the oven to check what it even looks like, making it worse!
So there you have it; a little guide on how to ruin a cake from start to finish. I hope for everyone's sake that we all learn how to bake a half-decent cake, but I've never learnt my own lesson!