I have found that i have the most success when I can use something concrete, like Algebra tiles, and then model the same problem in algebra so they can see how the two connect. I have always found that I can model every concept concretely, though. Also, i find that if I simplify a problem to show them the "why" something works and then move that same process into a more difficult problem they can grasp it easier. For instance, when my algebra students are faced with making a common denominator in an algebraic fraction, I first revert back to basic fractions and we discuss the how and the why of getting common denominators and then we move back to the more difficult problem so that they connect that the process is the same. The most difficult part about all of this is time. Some of my students can see it once and get it. Others need to see it 20 times and balancing the time it takes to help those students while not holding back my quicker students is a huge challenge!