Your goal in these workouts is to deeply fatigue targeted muscle fibres in order to create a stimulus for them to rebuild and grow stronger. You accomplish this by keeping constant tension on the targeted muscle(s), moving at a slow, even tempo, until you reach the point where you cannot finish the movement without breaking your form. At this point, you can try to use momentum to complete the movement, again while maintaining perfect form. When at last you can generate no further movement, you hold the weight under a static contraction for ten seconds and then slowly, and with control, lower the weight. The rest of your body remains relaxed throughout.
The body is efficient and will not generate new muscle tissue until it is really needed. Initially, it will respond with neurological adaptations to increase strength without changing the size of the muscle (by improving coordination, for example). In order to achieve the desired adaptation response, muscle fibre must be fatigued or stressed to a sufficient level.
Assuming you are practising good technique at an effective level of intensity, you can count on getting stronger, week by week. You will see results if you train once a week, but twice weekly is optimal. When training at this level of intensity, the number of exercises you are able to complete per session is limited: the best approach is to target larger muscles in one session and smaller, stablilizing muscles in the next. Your body needs at least 48 hours between workouts to recover and rebuild muscle.