Finding driftwood:
Look for hardwoods such as oak,mopane,honey locust,acacia,Hickory,cedar,ironwood,eucalyptus (soaking required to remove oils with eucalyptus),manzanita etc.
If finding wood on land look for dead wood and remove bark,avoid overly toxic trees like machineel, softwoods and cottonwoods rarely last long in water. Soak in water for several weeks.
If you are looking to collect wood that's already in water,feel the wood, it should be a piece with little or no bark,and should be hard,it shouldn't be crumbly or spongey.
Avoid collecting in areas with toxic chemicals.