The secret? Or at least mine, is Bondo body filler. It works like magic. A fellow furniture filpper mentioned I should try it. Once I did, I never looked back. LOL. Bondo is traditionally used in collision repair for dents and such. It’s not only very strong; it's also easy to work with. Just make sure you are wearing gloves. It sands down easily and if you are handy with an exacto knife, you can even carve out details to match moulding. I use 3M Bondo brand. You can buy it at Wal-Mart or your local automotive store. It works great. There are more premium brands available but they are pricier and I feel like the 3M brand does the trick just fine. There is a 3M All Purpose Filler. It's basically bondo too and can be purchased at home improvement stores. That works fine but the body filler seems to be more user friendly for me.
Both products require you to mix in a hardener. I suggest mixing small batches until you get the hang of it. There’s nothing worse than your filler hardening up right in the middle of a project!
I recommend mixing a small amount at a time. You do not want it to dry out on you. Patience is the key on patching a rough piece of furniture. The body kits comes with a red paste that needs to be mixed in. The red paste is the hardener. DO NOT FORGET TO MIX THAT IN... I use a paper plate or a spare piece of cardboard to mix the bondo on. This make it easy to discard any unused filler when you are done with the project. Use a small putty knife to apply. I also use my finger to fill in those tighter spots just to make sure the bondo is in the crevasses of the veneer. Once the bondo hardens, making sure those crevasses are filled will make it smoother and more seamless when it's sanded down. I use a paint stick to smooth it out and make it as level as possible on the surface. Do not worry about making it perfect. The beauty of this is that it all sands down later. Once it is fully dry... I mean really dry. (Do not sand if the area is still soft.) You can sand the bondo down. I recommend using an 80/120 grit first then work your way up-to a 220/320 grit. Once you smooth out your filler, you can paint your piece. That'st it! Easy peasy.