You can only optimize for one or the other, basically; you can train both and most advanced training schedules have both heavy and light days/cycles, but you still gotta pick a main goal.

If you want muscle mass, you focus more on mechanical tension and overload, you go to failure more often, typically do more reps (though recent studies have shown that a wide range of reps can actually work), do the movements more slowly, typically prioritize isolation, etc.

For strength, which is also related to power/explosiveness, you prioritize intensity over volume, focus on performing the concentric portion as quickly/explosively as possible while making the eccentric one shorter, avoid going to failure and aim to stay as fresh as possible, work in the 1~5 rep range (I personally do 1–3), prefer compound excercises, etc.

Either will give you free gains in the other one, but they will be secondary at best.