I'd suggest the following strategies:
(1) Revise Odd / Even rules, Number line concept, Types of Numbers (real/integers/rational/irrational etc..)
(2) Go through your concepts of LCM, HCF, Factors
(3) Revise rules for divisibility
(4) Go through some special properties (eg: the power to which 11 is raised will determine its tens digit 11² = 121)
(5) Go through square and cube roots, how to rationalize denominators, basic exponent properties, reduce fractions, convert into decimals and vice-versa
(6) Go through OG (or Manhattan Strategy Guide chapter-wise) and list down the different TYPES of Number Properties problems that are likely to appear on the GMAT.
(7) Keep practising each type
(8) Keep coming back to BTG and see if any member has posted a Number Properties problem. Go through the solution or be the first to post a solution (if feeling confident enough)
Hope that helps! Let me know if it works :-)
