Cake leveling is a big part of cake decorating. If your cake is not well leveled it will look unbalanced and if tiered it will probably loose it's balance!! While there a number of techniques out there here is what I have found myself doing over the years:
Level slicer for layers
How to Level a Cake:
1. Bake it:
Fill your cake pan 1/2 full of cake batter. When your cake is baked your results should look similar to the picture below with a cake dome above the edge of the pan. Let it cool for at least 10 minutes but no more than 1/2 hour. This will give the cake enough time to settle into the pan and just enough time to not be difficult to get out cleanly. Using the pan as your guide slice of the cake top/dome as shown. You will get the best results with a nice long cake knife. Also, be careful as the pan will still be hot. I always like to fold over the cake top when I am done to give the cake a good inspection. I like my cake to look spongy, soft, and moist. Whenever I have 'messed up' my formula oh man does it show!! (And if it's bad... I do it all over again!!)
2. Flip it! Right after it is cut it's time to get the cake out of the pan. If you wait too long the cake becomes more difficult to get out as it starts to settle in the pan as it cools. I like to wait 10 minutes and no more than 30. I also like to use trays to move the cake layers about. So with your plate, tray, or cardboard, place it on top of your freshly cut cake and flip. Be careful as the pan will still be hot.
3. Mark it!
I like to use edible ink pens to mark one line across the height of my cake layer. In this way, when I use the leveler to slice the 2" layer into two 1" layers I know exactly where they matched up. This gives me the best chance of keeping the same even level the cake came out with from the oven. So right after you mark your line make sure to use the layer slicer to cut your cake layer in half (sorry forgot to take a picture of that!)
4. Fill it!
Whenever you are ready to start the decorating process is when you are now ready to start filling. I like to do this after it has chilled for a few hours, that way you will get the least crumbs and great cake firmness to work with. The cake will also be more moist when you eat it! Fill between each 1" layer that you have created. Use the cake lifter to separate the the 1" layers. You can see that each layer will have it's own marked line. I also notice sometimes my smaller tiers like to bake a little of center. This is where I rotate the top 2" layer from the bottom 2" layer to get the most 'level' looking results.
5. All Level now Crumb Coat it! Now that you have a level cake - Congratulations!! To start the crumb coat cut off any unsightly cake 'bulges' on the edges like the lip that formed here. Using your cake knife cut these parts off. With that ready give it a good crumb coat to prepare the foundation for the final buttercream coat or fondant. There are occasions when the cake is still not quite level, in these situations use the buttercream and a good eye to create the look of a level cake by filling in any voids and removing excess at high points.
Good luck and thanks for reading!!