This really varies with each individual's goals. In my run/walk program, we begin very conservatively with a 1 minute run, and 5 minute walk. This run/walk cycle is perfect for someone just starting out in a running program.

The most popular walk break used in run/walk plans is a 1 minute walk break; however, depending upon the duration of your running interval, runners need to gradually "work down" to this shorter walk break.

The great thing about the run/walk strategy is that you can really "tweak" the run/walk intervals to fit your own fitness level and ability.

If you're going to use a 1 minute walk break, I recommend using a 1-4 minute running interval. You really won't find any improvement in performance or speed going beyond 4 running minutes, but as running minutes increase, the benefits of walk breaks diminish and the injury prevention factor is progressively diminished.

I've found that for women in my beginning program, the favorite intervals are run 3 minutes/walk 2 minutes (3/2) and run 2 minutes/walk 2 minutes (2/2). For intermediate runners, those training for a 10K, the 3/1 interval wins hands down!

I hope that helps!
Happy running!