Don't expect to understand your efficiency issues by taking a hydrometer gravity reading right before pitching yeast and discovering you are low, high, right on. A refractometer is a required piece of equipment in my opinion. Get used to taking readings on your batches as you learn your system. I would highly advise using beersmith and using the default efficiency as a start which is in the low 70s. Take refractometer readings during first runnings, the sparge(s), pre-boil, and before pitching. There are places in beersmith to add these values. If you brew a recipe from beersmith you can see how you stack up against the original. You can go back to recipes and check on progress. After several brews you can then set your efficiency based on collected data. You'll know what that is after some time on your system.
I would only use the grain called for in the recipes. If you're low and you have some gravity readings you can then begin to troubleshoot. Maybe the sparge runnings are lower than they should be. You can then look at that part of your technique. There are a bunch of things that can help your gravity come up. Looking at water, the crush, technique (huge), and more practice on your system are a few things that will boost your efficiency. If you throw more grains at the problem, do that when you are consistently hitting efficiency numbers and you're happy with it.