Having interesting holds is going to make your wall more interesting. Below are some things that you can think about and apply regardless of whether you are designing and making Wood Holds or Polyurethane Holds.
Creating Sets
What does the full set of holds you want look like? What hold types are you missing or need more off?
One method of setting a spray wall is to split the area into Zones with the same number of each type of hold in each zone. This then lets you set an all jugs problem or an all crimps problem over the same area of wall. Do you have the right balance of holds to create zones?
Small walls require a high density of holds to let a variety of problems or routes to be set.
Matching to your wall
Holds should work well with the size / amount of space the intended wall takes up.
Will your holds work for the angles of your wall?
Large volumes in a small space create short term interest. Initially a large volume creates an interesting problem but often getting round or over the volume results in very similar moves regardless of the holds.
Is the space used for something other than climbing – large volumes could be annoying if they stick out too far.
Variety
The greater your variety of holds the more interesting climbing on them is going to be. As well designing a wide variety of shapes you mix different construction methods and mix your holds with commercially bought ones too.
Different people come up with different ideas when designing holds. Variety is only going to help make your wall more interesting.
When making PU holds it doesn’t take long for someone to carve a shape in foam and everyone loves adding their initial or a “tag”. A home wall peppered with holds designed by friends makes for a good talking point and people love coming back to climb on holds they designed!