First of all you need to know about the plumbing symbols on a blueprint. You can learn about the symbols either by searching on the internet or getting information from a book. You can get plumbing related books form the local library or buy from a bookstore in order to know about the several symbols which are used for plumbing on blueprints.
Place the blueprint on a flat surface
Then you need to open the blueprint and place it on a flat surface such as tables, counters or any other plain surface. Open the blueprint so that you can read the whole page at once. You should have a knowhow about these drawings and should focus on the areas where plumbing is more focused.
Next you should familiarize yourself with the schedules which come along with blueprints. These schedules will tell you which materials are required for the particular project. You should check out which symbols are used so you can get those materials.
Identify symbols for major fixtures
After reading the schedule accompanied by the blueprint, you should check out which symbols are assigned to major fixtures. You should check the plumbing symbols for sinks, bathtubs, showers and toilet and then trace the drain lines from them. Remember you can always check from internet or a book for the symbols you are not sure of.
You should also check out symbols for gas lines, radiant heating water pipes and sewer connections as a plumber needs to know about these things as well.