I’m looking to make improvements on a home to increase value. My question is what should I spend 20 on to get the most return on investment.

Anything involving the kitchen and bathrooms are a good bet. You don't need to go too crazy because its easy to go well over 20k in these rooms. Cabinet refacing, appliance switch outs etc. Also look at what is popular in your area and check out local listings online. You can get an idea of what the trends in the neighborhood are. 

@Edgar Cabrera Rodriguez the thing that adds the most value is square footage by far.  But this also will likely cost the most.  I think the suggestion above is a good one so I'll add the following items are NOT good for adding value:

• Windows
• Roof
• Foundation
• Plumbing

The main reason here is because all of your comps will already have a roof, foundation, plumbing, etc. But they may not have granite counter tops, or nice flooring. You wont' get a $1 to $1 exchange on just about ANY renovation that you do. So it's really important that you are buying a property well below market value. Most will say you should be buying and rehabbing at 75% of the ARV. Admittedly, those will be hard to find but that's what most will say to target. Hope this helps!