How far apart should straps be place on electrical metallic tubing conduit?

Assuming your local jurisdiction adopts the NEC as code, EMT must be fastened within 3 feet of each termination point (box, cabinet, conduit body, etc.) and every 10 feet of conduit run. Where the (horizontal run) EMT passes through a hole in a framing member is allowed to count as a support in lieu of a strap. You can place fasteners closer if you want, but not further apart.

There are two exceptions.

#1 You can increase distance "within 3 feet of a termination" to 5 feet where structural members do not readily permit fastening within 3 feet.

#2 For concealed work in finished buildings or prefinished wall panels where such securing is impractical, unbroken lengths (without couplings) of EMT shall be permitted to be fished.

Reference 2005 NFPA 70 (NEC) 358.30(A)(B)

Of course if you do not live in the US, or if your local municipality has adopted a different code or adopted the NEC with ammendments, your local law could be different. Check with the local building department to be sure.