Calculating Percentages

[The_Missile]

I've been playing for over two years, and I'm pretty good with reading other players and basing what I have against what I think they have. But as far as percentages go, I'm never truly certain as to the exact percentage, except for obvious ones. What would you say could help me to be able to calculate percentages in my head? Thanks.

[GrandmaStabone]

read a book