This one is set to take place approximately 30 years after Return of the Jedi (which was itself approximately 1 year after the events in The Empire Strikes Back).
Ep. I is set approximately 35 years before Ep. IV, A New Hope.
Ep. II is set approximately 22 years prior.
Ep. III is set approximately 18-19 years prior.
Ep. V (Empire Strikes Back) is 3-4 years after.
Ep. VI (Return of the Jedi) is approximately 1 year after that.
Ep. VII, the new one, is approximately 30-32 years after that.
TAC, if you are planning on seeing the new one, do yourself a favor and watch the originals in Machete Order (which I described earlier in the thread). Watch them in this order: IV, V, II, III, VI. Skip I altogether. Then see the new one.