Answer by Elise Tucker Neilson:
Start two days before you need it to begin with.
Then, it depends on how adventurous you want to be. I would recommend starting with a box cake. They are simple, easy to follow and usually turn out with a great flavor (avoid cheap ones from Aldi's, etc. – stick with Duncan Hines or other brand name. I love a good deal, but have had some bad experiences).
Are you wanting a round cake or a square cake? For a round cake, you will need 2, 8-9 inch round pans. For a square cake, just one large cake pan will do the job.
Preheat the oven and go ahead and oil and flour your pan (take some oil on a paper towel and rub it around the pan on the inside until all surfaces are covered on the inside, then take a tablespoon of white flour and shake it around the pan until every surface is lightly dusted – throw out any excess flour that isn't stuck to the pan).
If you are afraid of the cake drying out, try replacing the oil in the cake with applesauce. Not only is it healthier, but it keeps it from drying out! So, if the cake mix box calls for 1/4 cup of oil, use 1/4 cup of no sugar added, flavor free applesauce.
Stir thoroughly, but don't over beat it. You just want all the mix, eggs, water, and oil to be thoroughly blended.
Bake as directed on the box, but check on it about 5-10 minutes before it is supposed to be done. Check on it by using a clean butter knife in the middle of the cake to determine if it is done – if the knife comes out shiny and clean it is done – take it out! If it still has uncooked batter on it, give it a few more minutes (close the oven door GENTLY – if you slam the oven door it will cause the cake to flatten).
Once done, take out and let it cool (NOT on the stove top).
if you want a polished looking, decorated cake, once the cake has cooled completely, place it between to sheets of wax paper, place in 2 gallon freezer bag (or larger, depending on your cake) and stick in the freezer overnight.
Once you are ready to decorate, pull it out of the freezer and decorate away. Don't wait for it to thaw! The icing will spread much easier if it is frozen (of course, allow yourself 7-8 hours before SERVING it, so it can thaw). Stick it back in the fridge until you are ready to serve.
Personally, I think it is easiest to decorate on a FLAT surface (no plates!). Any cardboard, but into the shape of the cake with about 2-3 inches extra on every side, then covered in aluminum foil does the trick for me and looks halfway decent as well.
Piping bags are always helpful if you want to write a message or add embellishments, but you can always use pre-packaged decorating materials as well.
I would suggest checking out a craft store for any decorations versus the grocery store – they will have a lot more options for you.