Choose indexes based on the kinds of where clauses or joins you perform. Choices for clustered indexes are:
The primary key, if it is used for where clauses and if it randomizes inserts
Columns that are accessed by range, such as:
col1 between 100 and 200
col12 > 62 and < 70
Columns used by order by
Columns that are not frequently changed
Columns used in joins
If there are several possible choices, choose the most commonly needed physical order as a first choice.
As a second choice, look for range queries. During performance testing, check for “hot spots” due to lock contention.