Make available liberal points of 0V and Vcc around the board. Sometimes the placement of cap's is enough but sods law dictates that the ONE signal you want doesn't have a convenient GND nearby, or when you need to add a cockroach mod there isn't a nearby power.

If you are going on to a small production run, consider identifying every net that doesn't naturally connect to an external connector, and connecting it to a pin on a ribbon cable header. This can be a lower budget option than adding test points for a "bed of nails" fixture.