Form does definitely help you engage the most muscle and lift most efficiently and it's a complex thing. For strength though what's helped me has been upping my volume (I used to do too many triples/doubles/singles in my programming). I like most of my workouts to be 5x5 @ 80% of my 1rm.
If your 1rm is 75kg try 5 sets of 5 of 60kg, with 4-6 minute rests. I'd also try working up to: 4x70kg, 3x72.5kg, 2x77.5kg, 5 sets of each, 6-7 sets of the heavier ones, over the next 1-2 months. This is what I do anyway. Always leaves me sore and has been adding 1kg to my bench per week.