It's possible to get strong and build mass at the same time, but the two have some very unique differences. That means maximizing one requires limiting the other. Here's how you should be training for each.
Choice 1: Build Maximal Strength
This goal has a large neural association with it. Repeated efforts and specificity are a big part of building a particular lift. So if strength is your main goal, then decide on that and build your program around the lift(s) you want to improve the most. A large degree of your time and energy in the gym will need to be spent just doing those lifts to maximize efficiency with them.
Lower reps with a high degree of speed and large amounts of volume are usually best when trying to accomplish this task. But if you're chasing numbers, you'll need to decide how you're going to set that phase up. Here are some examples for the big three:
- Squats 5 sets of 8 at 65-70% of 1RM (one rep max)
- Deadlifts: 3 sets of 3 at 75-80% of 1RM
- Bench Press: 5 sets of 8 at 70% with 1-2 back-off sets at a reduced intensity (60%) for as many reps as possible.
Choice 2: Build Maximum Muscle
On the other hand, if you want to get as massive as possible you must learn to isolate muscle groups effectively, feel the muscle do the work, and create as much tension as possible in the area you're working.
There's a huge difference in these two ideologies. A bodybuilder doing bench presses will try to FEEL the pecs doing the work. If building mass is the goal, then moving maximal weight for 1-3 reps isn't the most efficient method.
For hypertrophy, do 3-5 sets of 8-12 for upper body work, and 3-5 sets of 12-20 reps for lower body work (after warm-ups, of course). This is just an example of a size-focused program, not a hard and fast rule. You may also benefit from things like 100-rep sets depending on what the movement is and what you're trying to accomplish. Try starting with 4-6 exercises per training session to address areas that need the most work.
Determine what to focus on first so you can program and plan accordingly. Base your entire training structure around one: size or strength. Not both. Sure, there's some overlap, but choose one to focus on and you'll be much more likely to achieve it. And if you want to switch later, you can.