What kind of accuracy are you looking for, and what ranges? For most sporting reasons, I don't find it worth the effort. I find the most important factors for accuracy to be the powder type, and charge weight. I try to find the powder most suited to the cartridge and bullet weight I want to load, and work from there.
As far as case prep. helping groups, the most important I've found are making sure you trim and chamfer when needed This is especially so with new brass. Having trimmed all the case necks to the same specs help them hold or "grip" the bullet with better consistency. When starting with new brass, I neck-size first, then trim and chamfer. As a rule of thumb when you're going to trim the cases, do so after resizing them. After that, they're ready to go in my books. For the record, I've never had a problem achieving good groups under these lines.