The use of differing ways to distinguish intensity and volume can sometimes be an overlooked variable of training. A new, or new to me version is called RPE or rate of perceived exertion used to describe the intensity of load. Another option is the use of percentages of your on rep maximum. A easy example to remember is 80% of your one rep maximum would put you at about 8 reps. Along those same lines is the Rep range system where you define your intensity by reps you will be staying within 1-3 or 3-5.
(You don’t have to read this as it is in depth for some people to the point it may bore you) The above example help to the lifter define a intensity and energy systems that you are working within. There a multiple ways to look at energy systems. Energy systems for example are ATP system that fatigues in about 1-5seconds the creatine phosphate system that can fatigue in 10second or so. There is questionable beliefs and methodologies that explain what the optimal for training progression. Anecdotally, I find that staying within a certain energy system within phases is the best way to approach a progression. This is called periodization. I have discussed the idea of schizophrenic type training where no variable is clearly defined and no long term goal is being trained for, basically madness without means. Sometimes I think people just train to get the endorphin rush rather than define a long term goal. I get stuck in this rut from time to time. Either be it from stress, or busyness or just life priorities getting in the way.
All the above being said there is a lot that can go into planning. In many instances the acronym KISS applies. ( Keep It Simple Stupid) In many instances people will overcomplicate what they do, which can lead the individual to feel like they are not making progress. All of the above systems work though I think the most specific day to day one is rep range for me it is the one I have used the most. I have seen people use the percentage system specifically coaches who write team programs and have great success with it.
With RPE I think it is valid and useful for people who are not trying to tax the nervous system by tracking how close to failure you are each set. However the very worst thing a person can do is not keep track of weight sets and reps. So if you aren’t writing down what you are doing you are making a mistake. For female client I recommend a fufu journal, they can bedazzle if they have time. For males I just recommend a legal pad or one of those 3 hole folders because they only require college rule paper. Techie people can use a phone app but there is something satisfying about putting pen to paper.
In synopsis use what you like to define intensity, but be certain to record as the Chinese proverb goes “The palest ink is better than the best memory.”