Depending on what type of split you've had up till now I say try a full-body routine 3 days a week. Choose three different exercises for each bodypart and create a rotating schedule with those and different rep/set combinations. For example, for quads you choose squats, legs presses and
sissy squats. For the Monday workout do 8 sets of 3 of squats, for Wednesday do 2 sets of 20 of leg presses and for Friday do 3 sets of 10 of sissy squats. You'll get plenty of variation and you'll introduce a new stimulus with the increase in workout frequency.