1. Learn to convert opponent's argument to "premises+conclusion" form and challenge premises.
This is probably the most important ability to learn. Basically, when you have opponent's arguments written as premises, it becomes much easier to negate them since you clearly see what needs to be negated.
2. Use rule of three
Rule of three has many forms, but most common one is three sentences supporting one point. It works the same way as "2 premises + 1 conclusion" per point. It makes your arguments sound good even if they are retarded.
3. Write down all general arguments
The simplest possible way to prepare for all debates at the same time is to write down arguments which can be used in all or many debates. For example, argument of improving health can be used in many cases. Basically, when you write down lots of general arguments, you already have lots of material for all future debates.
