I'll just go ahead and describe a few things and give what hints I can. This will be aimed at the beginner but if anyone wants any more advanced info I'd be happy to help out.
If you have a rope with a bit of stretch try using a shorter span. Otherwise get a better rope. A prestretched yachting rope works well. I use a 10mm Kevlar rope - <1% stretch at half it's breaking strain of 3 tonne I think. I always work with bare feet and have no problem but then I do have rather tough feet.
Everyone has their own idea about how much of a loop (how much slack) to have in their rope. Lets call this loopiness the 'drop', measured as the vertical distance between the ends of the rope and the bottom of your foot as you stand in the middle of the rope. I usually use a drop of about 1 1/2 meters because it is easier to set up (you don't have to climb the trees to tie the ends up, you just tie them at head height). It's a good idea to try varying the drop in your set up. It's good for your technique (like varying the height of your juggling tosses) and you might find you have a particular liking to a certain drop. I have an idea that the ideal drop is equal to the length of your leg. But then of course there are tricks which are easier with a larger or smaller drop.
When starting hang the rope so the bottom of the drop is around 10 cm off the ground. The reason for this is that it makes falling off less of a trauma and because stepping up onto the rope is the hardest part. The shorter the step the easier. Note here that if you have a helper it's better to have the rope higher off the ground. You can use your helpers shoulder and get lots of practice at stepping onto the rope without endangering yourself too much.
As with all balancy things stay tall, look ahead (say at the knot in the end of your rope) and extend those arms out to the side. With slackrope work most of the balance is done with the legs, from the hips. So if you already use a tight rope you'll have to retrain yourself to take the emphasis out of your upper body and into the lower.
For basic walking I stand with my feet pointing slightly outwards so that the rope runs down the middle of my big toe and towards the outside of my heel. You might like to have the rope between your big toe and the next to feel more like your hanging on. When taking a step get your balance on one foot then point the other with your soul facing inwards and find the rope with your toes. Slide your foot along the rope as far as you want to step then adjust the foot onto the rope and transfer the weight. Now lift the other leg to the side to gain your balance again. As you improve you can reduce the time you spend on one leg until you are almost walking normally. If you want to walk fast turn your feet outwards more so that the rope runs across your foot somewhere between the heel and toes. This gives you more room for error during that fast walk. It looks messy though so save it for the fast work.
The frame has a post at either end connected by a cross piece just above ground level. The ends slope out about 15 degrees off vertical I think. To stop the thing from falling sideways it is mounted on a 1 1/2 meter length on either end.
\\ //
\\ //
\\ //
\\ //
\\ //
====================================
H H
The H's represent the legs which are 1 1/2 meters long and run into
and out of the page. The cross piece is made up of three 2m lengths
and a 1m length which fit together with sleeves. This way I can vary
the distance between the poles to suit the room available. Each end
pole is 2m long and slots into a sleeve. The piece above the H looks
like
\\
=========
-- a 2m long with a metal plate welded where the leg (H) attaches. The
elbow (\\) bit is welded on and is about 1 foot high. All the sleeves
have an overlap of a bit under a foot. The legs have a few screw holes tapped into them to screw them onto the plate on the above piece.
The rope attachment is a clever little gadget which fits neatly over the poles. They will stay at whatever height you put them simply by the weight of the thing making it hang onto the pole. It looks a bit like this:
__||_____
! o|| O !
!__||o____!
||
|
Pole
The o's are rods welded between two plates (only the back plate is
shown). The O is where the rope attaches. Weight pulling down on the
O will push the two o's into the pole thus gripping it. This system
has the advantage of being very easy to adjust. The whole thing can be dismantled very easily into straight pieces no longer than 2m long.
The cross piece must be a little off the ground or when you step on the rope the forces will tend to pick the ends off the ground and you'll have a very unstable situation.
I find this system works well for me but I wouldn't let a beginner lose on it unaided. The cross-piece is a little dangerous on those ankles. There is a bit of give in the whole thing so you get a rather bouncy rope but that can be fun and is no different to using a rope with a bit of stretch (without the dangers of using a stretchy rope).
I hope this has been of some interest and help to people out there. I'd hate to think I went to all that trouble for nothing :-)
Good luck.