A great way to learn how to perform kegels is while sitting tall on the edge of a hard chair. In this position, you can really feel your tissues firming up and then softening as you contract and release.
After women get good at simple Kegels, then it's helpful to add a co-contraction of the Tranverse Abdominis, or TvA. This muscle is our body's internal "girdle" and when contracted, compresses the abdomen.
All pregnant women should strengthen both the pelvic floor and TvA to prevent common pregnancy related complaints such as diastasis recti (abdominal separation), back pain, and pelvic instability. As an added benefit, because the TvA is the primary expulsion muscle, maintaining strength in this muscle greatly aids in the pushing phase of labor.
It's a myth that too much strength in the pelvic floor muscles can impede labor.
BeFit-Mom