We start by making the basemap frame for a linear x-y plot. We want it to go from 10 to 70 in x, annotating every 10, and from -3 to 8 in y, annotating every 1. The final plot should be 4 by 3 inches in size. Here's how we do it:
psbasemap -R10/70/-3/8 -JX4i/3i -B10/1:."My first plot": -P >! plot.ps
You can view the result with ghostview plot.ps.