Okay, I promised a discussion on avoiding ladders when working with DPNs, and here it is.
First, for those not familiar with the term, what is a ladder? A ladder is a loose spot in your knitting, between the last stitch on one needle and the first stitch on the next; the slightly long strands of yarn between the two stitches looks like the rungs of a ladder. Really severe ones can look almost like a dropped stitch, and even milder ones are not a particularly desirable feature. They're definitely the biggest concern of DPN users once they get over the initial hurdle of figuring out how to use them at all.
What causes a ladder is the strain on your knitting as you go from one needle to the next; the stitches simply want to pull apart there. Many people find that it's worse when they use a set of 4 needles than when they use a set of 5, because the sharper angle puts a greater strain on the corner stitches, so switching from 4 to 5 may be a fix. It's also common for it to be a worse problem with a slick yarn than a more grippy one where the stitches will hang onto their neighbors a bit.
If ladders are mild, the best solution may be to do nothing. Slight ladders often will even themselves out, when the item is first washed and blocked, and may be helped along by a little careful easing of the stitches on either side of the ladder if any looseness remains.
If the problem is more severe than this, here are some tips to ladder-free DPNs:
Pay a little more attention to the join point itself; snug the last stitch of the previous needle right up against the first stitch of the current needle before you wrap the yarn for that first stitch. Don't yank the working yarn here, but just make sure the bases of the two stitches are close together.
When you wrap the yarn for the second stitch, before you pull the old stitch off the needle, give the yarn a little tug; repeat this on the third stitch if you feel like it. Don't yank on the first stitch, and for goodness' sake don't yank on the last stitch of the needle, which tends to make the problem worse instead of better.
These first two things are usually enough to eliminate your ladder issues; give those a try before you take more drastic measures. Some more drastic measures to take:
Change the way you're coming at the first stitch. I really prefer the method I explained in the last post, where you come up from below and to the left of the next needle to the right, but some people with persistent laddering issues do find it beneficial to come at it the other way, from above and to the right. I don't like to do this because it disarranges your ends, which either makes them get in your way more or requires you to move them on every needle, but if you're having difficult laddering problems, go ahead and give it a shot and see what you think.
Shuffle your stitches. Some people find it helpful to knit the first couple of stitches of each DPN onto the DPN before it, instead of immediately switching to the free needle. This causes the beginning of the round to gradually migrate around the circle of needles, so you'll definitely need to use stitch markers to mark the beginning of the round, and any other points that are important to your pattern, such as which stitches were originally on needle 1, etc. I'm not a big fan of this method, because it doesn't actually address the problem, only masks it by causing the loose stitches to be distributed throughout the piece instead of lined up in a column; I don't favor, generally, treating symptoms instead of causes, when the causes are susceptible to treatment. If you want to try it, though, it is a way to handle laddering.
Make a few swatches, and see what seems to work for you. With a bit of experimentation, you'll find the best way for you to produce beautiful, ladder-free work on your DPNs in no time.