How would I learn to write Oracle SQL queries?

Oracle/PLSQL 

this link will guide you to the basic functions and statments you can use in SQL language

and also supply examples for help

 

by actual work, by time, by facing new, varieties and some times difficult queries, ... so solving it make your experience more efficient, this will help you to turn simple sentences to a written query. actually you will find it difficult just at begging, but I encourage you to go on.

start reading the old9i dql fundamentals from oracle university ,that is the one of the best book for beginers. Else you can buy tata mcgrowhills red coloured big book named-Oracle SQL fundamentals

http://www.w3schools.com this site best for beginners.

First clear your concept in D.B.M.S and R.D.B.M.S. If you already doing some programming and wants to move/learn Oracle SQL Queries than visit www.techonthenet.com where you can find complete study solutions of Oracle Database. As you would start you would get the knowledge step-by-step and for detailed discussions you can join Oracle Discussion Forum.