My advice is pretty simple. Read books. Duh. Grammar through exposure is the best way to learn, and generally takes very little time if one immerses oneself in native material. I personally got through Genki 1 and half through Genki 2, and I can read japanese novels and manga with no trouble grammar-wise. Its most definitely not rocket science, just a matter of practice makes perfect. No need to get overwhelmed, as your brain recognizes the grammar patterns after enough exposure. My old way of doing grammar was to simply write down new grammar that I find while reading, look it up, do some practice with it, then let my brain sort it out.
Its worked quite well for me, considering I haven’t had to learn anything grammar-wise in over a year, and I generally read Japanese books every day. Not sure if that would be your preferred way, but its just what’s worked for me (currently N1 atm). By the way, if possible, I would recommend using Lang8 to write sentences using the grammar you find or have difficulty with, since native speakers can point out any mistakes.