While experiance is the best teacher and books like Means, Dodge-McGraw Hill and a few others can help, I would suggest a short course on construction cost estimating. A two, three day or week long course would jump start you on your way. Means sponsors some, the AGC and some university extensions have courses.
Using cost books, without some prior experiance, can be very troublesome. You have to know and understand the basic assumptions the cost books make for their unit costs. Many new estimators forget about the mobilization and demobilization costs, the jobsite office costs etc. You might find that the book tells you you can pour footing concrete for $145/cy, but what about hand grading, forming, stripping and hand compaction, besides the jobsite office and supervision.
Get some training!