RE: How do you warm up for weighted dips?
I normally do two warm-ups, one at 60 % & one at 75-80 %. I think it's better to include body weight in the warm-ups. So if you weigh 90 kg and your working sets are BW (90) + 20 kg = 110 kg, 60 % would be 66 kg. Obviously you'd have to use an assist machine for this.
Using Bodyweight might be too heavy for the first warm-up if it's your first exercise....