I found a good protocol that worked well for the DB press. I would start off with 3 sets of 10 with the same weight, resting about 1 minute. Do that 2-3 times a week. Then the next week I would keep the same weight but add 1 set. Then the following week same weight but add one more set. Either keep the rest the same or if you really want to make it more brutal decrease the rest by 10-15 secs each week. The weight was not that heavy, about 60-70% of what i could do for a set of 10. The same time I was doing this I was also doing a lot of bench pressing (Sheiko routine to be precise), I did this after the sets of bench. Even still the first week the weight feels quite easy but don't go up and focus on form, the extra sets and shorter rest add up.
Here is an example
Week 1) 70 x 10 reps x 3 sets (1 min rest) Do 2-3 times a week (Mon/Wed/Fri or something)
Week 2) 70 x 10 reps x 4 sets (:45 sec rest) Do 2-3 times a week
Week 3) 70 x 10 reps x 5 sets (:30 sec rest) Do 2-3 times a week
Week 4 or 5) Pick a weight and max out, I think I got 100 x 20 for 2 sets and failed on the third with 2 min rest or something like that.
I think you should focus on good form the whole time, I was doing mine with Neutral grip to better mimic the path of the bar on the bench press (although when I did the max week I did regular grip). I also think improving your bench press helps increase your DB's a lot. Don't cut the ROM short. Good luck