tune an execution plan

Dear all,

I have a general question about tuning an SQL Stmt using it execution plan. if you know nothing about the DB and what it contains ... you know nothing about the tables where the stmt is running!

you just see the Stmt and it execution plan! is it possible to comment on it execution plan and give suggestion to make it faster? how would you do that ?

any execution plan could be an example for this discussion ... you can see the following plan, can you comment on it and make suggestions to make it faster/better ?

--------------------------------------------------------------------------------------------------------------------------| Id  | Operation                               | Name           | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |--------------------------------------------------------------------------------------------------------------------------|   0 | SELECT STATEMENT                        |                |     1 |   122 | 17372   (1)| 00:02:24 |       |       ||   1 |  HASH GROUP BY                          |                |     1 |   122 | 17372   (1)| 00:02:24 |       |       ||   2 |   NESTED LOOPS                          |                |     1 |   122 | 17371   (1)| 00:02:24 |       |       ||   3 |    NESTED LOOPS                         |                |     1 |   122 | 17371   (1)| 00:02:24 |       |       ||   4 |     NESTED LOOPS                        |                |     1 |    99 | 17370   (1)| 00:02:24 |       |       ||   5