I've learned today, if
Suggestion: READ THE MANUAL, at least once. The whole "option" thing is well documented, and you may be surprised how much else you can learn.
your query will run on multiple
processors and if it's huge query,
query will perform faster
No, this is not what MAXDOP does. Under NORMAL circumstances it does absolutely NOTHING. Get that - you learned hogwash ;)
Here we go:
The MaxDOP option defines the MAXIMUM degree of parallelism. It does not say "use more processors", it says "go maximum parallelism X" and if X = 0 that is the number of processors.
Here is the catch, though - there is a system wide setting for MaxDOP that already says 0, so under normal circumstances it does nothing in the way you want it.
What it is usefull for is to limit the max peralellism FURTHER for queries where it makes no sense (because no, it does not automagically make a query run faster - it can actually make it run a lot slower). In those cases specific uewries may like an Option (maxdop 1) to be llimited mor ethan the default setting does. You can read more on it at http://msdn.microsoft.com/en-us/library/ms181007.aspx
That being said, MaxDOP is a tricky bgeast to master - in 99% of the cases it makes zero sense to put a maxdop into a query.
What guidelines are there for SQL
There are none. Standard SQL principles apply (only ask for what you need, have proper indices etc.). The rest are rarely to be used options - so generic principles do not apply (as they are rare - generic guidelin: do not use them).
The guidelines are, btw., called the documentation.
Like always (your post is a very good example) limited knowledge pretty often is one thing: totally wrong (as you did not even know what MaxDop 0 actually does).