Considerations for creating indexes

Considerations for creating indexes
I got these tips from sqlservercentral.com written by Gail, I found them so helpful for new folks.

- Clustered index should be narrow, because the clustering key is part of all nonclustered indexes.
- Composite nonclustered indexes are generally more useful than single column indexes, unless all queries against the table filter on one column at a time.
- Indexes should be no wider than they have to be. Too many columns wastes space and increases the amount of places that data must be changed when an insert/update/delete occurs.
- If an index is unique, specify that it is unique. The optimiser can sometimes use that information to generate more optimal execution plans.
- Be careful of creating lots of indexes on frequently modified tables as it can slow down data modifications.

for more detils please check it out:
http://www.sqlservercentral.com/articles/Indexing/68439/