On habit to get into if you haven't already, when working with physical problems, put the dimensions on every number (assuming it isn't dimensionless and those are rare). Then you have two problems, one to carry through the math on the numbers and get a numerical answer. The other is to manipulate the dimensions and arrive at the dimensions for the answer. If the dimensions don't come out, it's usually a good sign that you've left something out or otherwise set up the problem wrong. This includes all the conversion factors needed to make all the values conform.
Also, learn to quickly at least figure out the order of magnitude the answer should be and if your final answer isn't in the ballpark, something is rotten in Detroit.
