I think that if you are doing hard exercises like bench press or squat by yourself and find yourself on the brink of acceptable form or even breaking form, then maybe it's not a great idea to increase the load next time, except you feel sure you will be able to do it. I often begin doing an exercise thinking that I won't be able to increase the load because it was just too hard last time. But much more often than not, it seems that the body just adapts faster than my mind and I am able to do more work than I think I am. So maybe you will be just fine? Usually when I am increasing my load, I just do so on one set of the exercise and see how it feels and if I think it is too hard I just grab the next (lighter) db. I feel safer doing so on the last set rather than the first, when I have warmed up thoroughly. Also, then I have more of an idea how it feels at the end of the set. I have this mindset of just finishing what I start, almost no matter what, and only occasionally I skip the last one or two reps to stick to good form but usually I just push through while trying my best to stick to good form.