It's amazing how many seasoned gym trainers don't do this. This is why people become highly susceptible to ongoing plateaus.
Related: Kris Gethin's 4 Step Guide to a Shredded Six Pack
You can do more sets, chase the pump and have an extra protein shake but really all you're doing is still guessing. That's the slow way to progress, start tracking things properly and you'll start seeing things change swiftly.
Tracking your training is a very simple process, it's simply a case knowing what weight you're able to do for what reps within what level of volume (total working sets) and you then aim to beat those numbers.
This is the most basic, fundamental way to bring about new gains into your life. This can be used with any rep range as well, high as well as low. If you get stronger on a 20 rep set you're still going to generate overload.
Gaining Muscle by Better Tracking
Beyond this you have to look at the number of working sets you're doing with the weight and reps in mind because this will give you the accumulative overload you've achieved. Maybe going from 12 sets with X amount of weight to 15 sets is enough to break the plateau, because across the workout you have done more work accumulatively.
It doesn't need to be more over thought than this, the essential bit is very much in the doing.
Nutrition is a bit more complex because there's not necessarily a "perfect" number to aim for and it is certainly more time consuming tracking food, all of the time. However if you're intent on breaking boundaries then just accept that this is part and parcel of the path you've chosen.
So many people are inaccurate in their estimations of what they eat, because they guess or forget to factor in "hidden" calories from drinks, sauces and that sort of thing. For the next 7 days get yourself a tracking app and weigh absolutely everything out which you eat.
This will give you true reflection of what you're actually consuming. From here it's a matter of deciding if you need more or less of the nutrients in your diet.
What I'm saying is that by knowing what your numbers are you're set for faster progress because it becomes a mathematical equation, using science rather than guess work.