Many instructions I’ve seen say that you should “catch” the yarn if you must cross behind more than 5 stitches; I like to do this anytime the gap is more than 4 stitches.
When you’re stranding colorwork, the strands as you hold them should stay in the same positions relative to each other - one closer to the work, one further away. I knit Continental style (with the yarn held in my left hand), so I carry one yarn over the top of my index finger, and the other yarn under it, with the yarn held under the finger being closer to the work. The yarn held closer shows a little more prominently in the design. See how the multicolor stripes look thicker in the light mitten than in the dark one? The cream was held further away, and the brown was held closer.
To catch the yarn float when there is a long stretch of another color, the relative positions of the yarn must change. So I knit to 1 stitch before the halfway point, then move the carried yarn between the working yarn and the fabric. If it’s the yarn you normally held above, move it down. If it’s the yarn normally held below, move it up. Knit the stitch, then move the carried yarn between the working yarn and the fabric back to its original position.
See the little dark lines in the large areas of blue and the little blue lines in the large areas of black close to the center circle? That’s what it looks like from the inside.
This may or may not be how others do it, but it works for me. I hope it is helpful to you, too
The patterns shown above, in case you were wondering, are Alesund (the mittens) and Harmonic Curves Tam (the hat).