Being: I think one of the most important things with dipping is that you should be comfortable during the movement. A deep dip is pretty hard on your shoulders and once you have worked up to adding 100lb or so to the movement you'll want to be sure you aren't going to suddenly hurt yourself because you can't maintain a certain position. So, just try to find a grip width that feels good to you; usually not too wide or too narrow will be good enough to hit your pecs hard and give your tris a blast too.
Get used to adducting your shoulder blades like you would for bench (although not quite as much); this will stabilise your shoulder joint during the movement. With just body weight it might seem harder to decide on how much torso angle to use but once you hang extra weight from a belt your C of G will effectively change and you will naturally compensate for that to some degree and find a groove that works for you.
Tipping your head forward a bit and looking down should help keep your torso angle from becoming too vertical, esp. once you start to struggle. Conversely, lifting your head and looking more forward or up will tend to cause a shift to a more vertical torso angle. Experiment and see.
Keeping your knees and hips bent a bit is a good idea. Assuming you don't have to lift your legs to keep your feet from hitting the floor then a comfortable bend is all that's necessary. Just keep them in the same position throughout the movement - no thrusting to help kip yourself back up to the top position.
Dips were tough on my AC and glenohumeral joints initially and once it got heavy toward the end of the 5s I used to feel as if I might rip in half during the turnaround (thankfully, I never did!). My advice is not to rush into adding too much weight too soon even if you feel able to do so; allow your body time to strengthen the various ligaments and insertions over a few cycles. You want progress not an injury.
Adding negs at the end of a cycle is easy with dips but, again, just be careful not to go too heavy too soon. For your initial post-5s you could take your 5RM load and do 3 or 4 regular reps followed by another 3-5 negs. You should find you can repeat that for a few sets and get some good strain going on. Then at the end of the next cycle you could try incrementing the load a bit beyond your 5RM and see how you feel doing negs with that.
I really hope you get on well with these because I think they're one of the best upper body exercises out there. Once you have them down see if you can find some oly rings to try dipping with. It'll probably be quite a shock the first time you try!
