When it comes to mounting things on walls, I'm a big fan of 3M Command Strips. I use large for most maps and signs; medium for medal holders.
Whatever size you choose, take 2 strips:
And place them together, with the tab at opposite ends:
You now have 2 sets. 1 set is sufficient for most projects.
Peel the backing off of the strip without the tab. That's the piece going on the project.
For a larger project or sign, you may wish to place the strip horizontally.
A dab of instant glue may be necessary for the strip on the wood - sometimes the wood is resistant to the adhesive on the strip.
For most projects I recommend centering the strip in the top 3rd of the project.
Place the other strip back with it's mate, . Just a light press is enough.
***Note this picture is showing the incorrect half - the strip with the tab should have been in the above picture, mated to the "untabbed" strip affixed to the back of the project.
After the strip has been affixed to the wall, remove your project, leaving the tabbed command strip stuck to the wall:
Press the strip against the wall firmly for 30 seconds. Wait 60 minutes before hanging your project. (This is per the instructions included with the Command Strips.