Playa's streets actually make sense and are easy to follow. La Quinta (5th Avenue) is Playa's main tourist area, a pedestrian only street surrounded by boutiques, restaurants and hotels. From 5th Ave (which is only a block from the beach), heading west (away from the ocean), the Avenues go up by increments of 5, so parallel to 5th is 10th, then 15th, 20th and 25th. The next avenue up is 30th, a main road where you will find MEGA and WAL MART.
The streets crossing these Avenues are in increments of 2's, starting at Juarez on the south end of town (closest to Playacar). From Juarez heading north, you will cross 2nd, 4th, 6th, 8th etc. Stop at 4th and walk up to 25th a block before the Wal Mart street