Read, read, read: books online, a web page or blog...

Practice, practice, practice...

Microsoft E-learning, plenty of free stuff there. Go to products > SQL Server. There's tons of free stuff (intro to 2008, What's new in 2012, BI Blah-blah...)

Install SQL Server Express, it's free (on a computer you don't care about while you're learning). Play around with adventure works. Make a new DB. Back it up, export a table, create a view, etc..

Want a real headstart?!?! - Begin a code library. This really helped me - you get some practice and can use it... Start with TSQL, make some notes, etc..

-- string functions

--REPLICATE

DECLARE @STR varchar(50) = 'xyz '

SELECT REPLICATE(@str, 2)

-- LEN (length)

SELECT LEN(@str)

SELECT LEN(REPLICATE(@str, 2))

SELECT LEN(NULL) .....

-- aggregate functions

SELECT COUNT(*) FROM sys.databases

SELECT SUM(a) FROM...

--useful system views

SElECT TOP 10 * FROM sys.all_views

SELECT TOP 10 * FROM sys.syslogins ...

... next go do one with MDX or whatever...