Well, you certainly wouldn't say "climb to FL50" as that could be misunderstood as "climb FL250".
The only guidance I received in the UK was not to give more than three instructions in one go and as orgASMic says, use discretion when issuing instructions to student pilots (and also those with a limited grasp of English or in high-workload situations).
In Canada, the format was generally heading, altitude, speed. Here in the sandpit, I generally try to stick to that although our flight progress strips have boxes for altitude, heading, speed in that order, so sometimes it comes out that way!
IRRenewal - you're perhaps being a bit obtuse there. "Descend 4,000" means "descend to altitude 4,000 ft" to pretty much everyone. When I was in the UK, it would have been correct phraseology to use the latter. Here, we use ICAO phraseology without the word "to", and I have yet to hear of anyone asuming a cleared altitude was an instruction to descend by, rather than to, the altitude given.