Only fill pan 2/3 or less. Any more and the batter may spill over and make a mess in your oven.
Before placing the pans in the oven, bang them down on the counter a few times. This will even out the batter and remove any air bubbles.
It is better to “over” bake than “under” bake. If you are not sure the cake is done, leave it in the oven for a few more minutes. However, this is not true for cupcakes because they continue to bake a bit while cooling in the pan. They should be soft but firm when you take them out of the oven.
Do not keep opening the oven to check on your cake. The repeated changes in temperature will cause it to fall.
Make sure the cake is completely cool before icing it.
If you own a Kitchen Aid stand mixer, you most likely find the ingredients on the bottom of the bowl remain unmixed. Buy metal washers at the hardware store and place one directly on each of the two prongs that hold the bowl. When you attach the bowl, the washers will raise it just enough so all your ingredients will mix but the beater will not scrape the bowl.