Crush and volumes. It's all about crush and volumes, 90% of the time. Fix those two things first. Don't trust your LHBS. Buy your own mill, or crush it twice or even 3 times if you need to, to get the grains milled down towards flour, while keeping the husks more intact. Volume measurements are very important as well. If you aim for 5 gallons post-boil but end up with 5.5 gallons, your gravity measurements will be off by 10% or as much as 5 or 6 gravity points, which is a huge effect when efficiency calculations assume that you hit the proper volume spot-on.