^I second this, but as an acc player I personally recommend playing really easy maps, like 1-2 star and try to SS them. Try to aim above 994k as well (I go for 996k+). If you can, try to 1,000,000
Pi by Jinjin. It's probably the easiest map to 1,000,000.
Also play with the HR mod for a bit and then play without it so that the regular timing windows feel looser by comparison afterwards.
Alternatively, you could (if you have Etterna) try J7 training, which is basically the same concept. If J7 is too tight for you, you can try J6. J4, if you're unaware, is the default judge, and J7's timing windows are half of J4's.