As normal condition, if there is SQL only, the RAM should be controlled under 40% or less, some peaks are OK. If the box is shared with others, ie. file server or mail server (the very bad situation is PDC), it is little hard to deal with RAM percentage.
If you have SQL only box, the high % RAM must be caused
by some LARGE processes, ie, DTS for huge file loading
or migration in nights. At this situation, you can use
SQL profile to detect one-by-one. Debug them if you have time, or reschedule them to a later time after your
normal backups if you do not have time to debug.
Try a way which has less affects to your system, this will help your job safety !