Knitting cast on methods
Choose a cast on for the edge: long tail for a flexible general edge, knitted cast on for adding stitches at an existing edge.
Work the technique
Long tail: make a slip knot with a measured tail. Spread tail over the thumb and ball yarn over the index finger. Pass the needle under the front thumb strand, over the index strand, then back through the thumb loop; release and tighten gently. Knitted cast on: knit into the last cast-on loop without dropping it and place the new loop on the left needle.
Try it on a sample
Cast on 20 using each method, knit four rows and stretch each lower edge. Count the initial slip knot as stitch 1.
Check and recover
A tight edge needs remaking before a full project. Keep spacing between new stitches; do not stretch just the needle loops.