First things first: you should pick ONE test and stick with it.
It’s always best to focus – these tests require vastly different strategies and approaches, and if you study for both, you’re just spreading yourself thin.
First, figure out which test is best for you using my free guide to the New SAT vs. the ACT. Once you’ve done so, start studying for the test that you prefer / that gives you the highest comparative score. Then make sure you’re giving yourself the proper time to study. Unless you’re in your senior fall, you shouldn’t just take a test “for the heck of it” – take a test when your practice scores match your target goals.