I normally do plenty of walk on a long rein to start to ensure my horse has stretched enough. Do trot and canter on both reins then walk to canter to get his back end truely engaged. Canter 15m & 10m circles to encourage good flexion and bend.
One trick I got from a magazine was to always jump an upright as your last warmup fence before you go in - encourages the horse to pick their feet up
With my horse (he's 17 now) I give him a walk and trot round on a loose rein and then get up in my stirrups and give him a good stretched out canter on both reins to loosen up his back. we were taught to do this at college and it certainly seems to work for him, then i will do work in trot and canter on both reins working him in circles and in an outline to make sure he's engaging his hocks.
Pop over a cross pole a few times at canter and then put an upright up and if possible a spraed with a cross pole in front and then to a parallel. Do NOT keep jumping and jumping. Providing your horse is warmed up and concentrating that is fien, it does not good to just jump and jump over and over til you go in
I am told by my trainer to jump a coupl of smaller jumps before i go in and as he is strong i stop him dead after the jump then go in he should be listening but I have to say he just gets so excited its a mission ( see mu other post about bit problems)!!!
Also do some rein back to canter to get them on thier hocks
i find it good to make as many different fences as you can, eg x-pole, upright with x bar, upright with ground line, parallel with a cross at the front, square oxer etc, but dont over jump, only need to do each one of these once or twice, but it means the horse has seen lots of different types before you go in, esp good for spooky/young horses
if its not too busy in the collecting ring, i also jump the jumps at a slight angle to get the horse concentrating, esp if its 2 phase or im getting ready for a jumpoff, but obviously thats pretty hard to do when your having to avoid lots of other horses to get to the fence!!
What size fo course are you jumping at the weekend? These tips all sound fantastic if you're riding a foxhunter track, however, if it a 2'6" unaffiliated course I wouldn't worry too much about flexions, backing up and screeching your horse to a stop after parallels, cross poles, verticals etc I would just warm up so both you and horse feel confident going into the area and try to have fun
I guess it depends on your horse - as above I like to let mine have a good stretch as he'll more often than not have had a trip standing in the wagon and, with him being 'middle-aged' a like to know his muslces are stretched out. Also seems to work to settle him down. we had some lack of confidence issues some years back following him having a back injury, so i like to make sure he's not tense before jumping him.
I don't ever do silly jumping - ie putting up stupid height fences though and hammering over them time and time again. My horse, in my opnion, knows what he's doing, he knows how to jump so my main thought is just to get his muscles warm.
One of my bug bears at SJ comps are the people who insist on going over and over the same fence time and time again and putting it up as high as they dare when they're only actually jumping say a 75cm course!