What is the best way to become a professional quantity surveyor?

The best way to become a professional QS is to learn from seniors and to guide the juniors.
Problems will be solving and the assignements will be accomplished in time.

Adopt any path of RICS.
After membership you will be certified QS and will enjoy a handsome package.

Techincal degree + site experience and follow the standard methods, RICS Membership additional tag

Try to get associate membership from one of leading profesional institute such as RICS you can get furthe information about RICS membership from following link http://www.joinmyapc.eu/

There are about six steps that are important to become a QS: 1-Understand the Duties of a Quantity Surveyor 2-Realise the Differences in Types of Surveying 3-Differentiate between the two types of Quantity Surveying 4-Decide if Quantity Surveying is your desired career based on Steps1 and2.
5-Have a study on becoming a Quantity Surveyor 6-Do not worry and Get a Job as a Quantity Surveyor  

to become a professional quantity surveyor a)every projects base on the specification, pay items detailed estimated quantities , b)copy of projects BOQ, c) shop drawings, d)site inspections base on executed works, d) As-built Quantities.
& etc