Josiah,
I have a Lansky I use with slipjoints. I've never needed to do anything much more than strop my FB knives at this point, so I can't say I've got experience there. Here's some things I've learned in the process.
1. There is some slack due to the design, as others have mentioned. Another solution I have found for the guide rod slack is to tape over the guide hole and poke a small hole through. This forms a grommet of sorts that improves the system.
2. Others have mentioned taping the spine to allow better grip. I did this earlier on, and then discovered taping the clamp itself seemed to work better. Ymmv, of course. I also (in flagrant disregard for the instructions) use a screwdriver to tighten the clamp with some knives.
3. Again, as others have mentioned, clamp as close to the center of the blade as possible. Since the angle changes constantly, clamping in the center minimizes these variables. Also, just expect that your bevels won't look even. Tips are thicker by nature on most knives, and the Lansky can't adjust for that the way you'd slightly raise the handle end when stripping or free hand sharpening. That means the bevel will be wider there than closer to the handle. This is also why longer blades don't work so well. I've done it on some cheap chef's knives, but the results weren't spectacular. I saw someone recommend buying a second clamp for longer blades, which seems like it should work.
4. I time sides instead of counting strokes. This is a tip I found online that seems to work better for me. 1-2 minute timer, flip. Repeat until the wire edge starts to form, then move up the stones.
5. This is a general sharpening thing, but it was really drilled into me with this system: spend most of your time with the coarsest stones. Nothing else in this system will work if your bevel isn't just right. I'm looking to buy a diamond extra coarse stone to aid in this step.
6. I get a consistently good edge. Paper cutting, hair shaving edge. Not a scalpel, hair tree-topping edge, nothing that competes with my straight razors. But an edge that is much sharper than the average person thinks "sharp" can be on a pocketknife. It's more than adequate for any uses I might have, though it will not satisfy someone who is really into being able to achieve the sharpest possible knife. My conception of "sharp" changed dramatically when I held a knife sharpened my McVeyMac which he described as sharp but far from the best I can do. Sharp for me is no where near his league. But it works for my purposes, for me, for now.
Something else may come to me, but I think that is the highlights. Happy sharpening!
Michael