How to drill into horizontal wood + drill though wall?

[OM2]

I need to drill onto a wall a horizontal pieces of wood (4cm thick).

What's the best way of doing this so that my holes are lined up?

The obvious thing would be to hold the wood onto the wall and drill?
That could be tricky as it need someone to hold the wood in place?
Keeping level is the other problem.

Drilling onto the wall first and then drilling into the wood seems NOT a good idea.
If not aligned perfectly, then the wood is not level?

Scratching my head over this trying to think of the best way.

Thanks.

 

[Trazor]

Drill and fix at one end only, then you can rotate the wood, as required, to level up with a spirit level.