Bodybuilding:About drop sets?

Either doing a specific set of reps as you say or doing till failure would be fine. I personally usually go for failure when doing drop sets. The point of drop sets is to shock the muscles, so it helps when you're facing a plateau (not making gains), and thus it would be best to not make it part of a regular routine (since it wouldn't work as well if done so and also because you may overwork the muscles).

As far as the reduction percentage is concerned, you can do anywhere from 10% to 25% (for tight drop sets) to even 30% or more (for wide drop sets). I go for 10% personally. How many times to drop the weight? Well, the Wikipedia article I read suggests that some bodybuilders would recommend no more than 3 distinct weights, but you can do it more times if it helps.

Oh, and, I noticed that you said that you started about a month ago? As far as I know, drop sets are an advanced technique for those who have been lifting for a while, at least more than a year, I would say, if not more. I didn't seem to need it when starting out. I would say that you should focus on getting your form as good as possible and completing the reps you have established with as good a form as you can pull off. When I started out, I was told to do 15 reps for the 1st set, 12 on the 2nd, and 10 on the 3rd. It gives you muscle strength, endurance and hypertrophy since your body is not used to the lifting. You can change these as you advance.

And starting out, don't focus on the weight, focus on the form. This is mainly for hypertrophy, but even otherwise, it's good to get a nice base first and then to go for upping your weights.

Cheers. Hope I helped. :)

Drop Sets Bodybuilding

You know drop sets... Yes it can help in some cases but it's not very important...

As a beginner (160lbs bench) you are focusing on micro-details here... Things like nutrition, quality of rest and volume/intensity of your workout is much more important.

Go for failure but count the reps, so you know next time whether you're improving, and have motivation to push yourself. Take it slow and give yourself lots of time to recover between drops, especially if you've only started working out recently, or you're just going to do damage.