My 
Weight lifting has become a HUGE part of my fitness journey, and I am still working on as well have improved on my nutrition which is major. I am fond of my home workouts for reasons I shall share later but my focus is on weight increase.
My workouts are with a trainer, and still at home. There is a sheet to record weights used and monitor growth and the trainer actually suggests when to increase the weights. I am good in following the trainers because they have more knowledge than I. However if my current weight use is still challenging I will not increase for reasons of : possible injury and compromising form to get the benefits. When I am able to lift, lunge or press with weights that are not challenging or I am able to do 3-5 more reps without feeling a challenge then I will increase my weights.
I know by how much well, this depends on what I have at home. There weights in between the 5 pound increase such as 10 to 12 instead of 15 or 15 to 17 instead of 20 and yes 20 to 22 instead of 25. Oh yeah I am speaking of dumbbells because I can increase in increments of 2 or 2.5 on the barbels. For me I have only that 12 on the dumbbells so I have to up my weights by 5 . Which I do with caution.
Cautious weight increase is important to stay on the journey without injury and to benefit from the challenge of increasing the weights. To a week of increasing weights and or reps with safety.
Nitrice Healthy Fit 