You should ~ as much as possible.

[Kid Chrono]

Is this eng-jpn translation correct, or is there perhaps another way to say this that would be better?

You should exercise as much as possible.
成るべく運動すべきです。

Thank you for any help you can give me :-) .

[nhk9]

narubeku is quite formal, u might want to use "dekirudake" instead. It's much more common.

Also, for subeki, you may already know that it's quite strong. maybe you want to try "shita hou ga ii" instead, which is much softer.

[Kid Chrono]

Thank you very much :cool:. できるだけ is something I will definately have to read more about.