How to optimize the performance of a very large MySQL database?

I am working on a web-application in PHP-MySQL. I am MySQLi API for database access. I have broadly two questions:

1. How can I increase the performance of the MySQL database?
2. How much secure and suitable is MySQL for large, enterprise level database?

For question 1, please note the following points:

• The main central tables of the database are expected to receive about half a million to one million rows every year. How can I speed up retrieval from those tables? I already have created Index on those tables.

• I am moving the archived rows to a new table, and keeping only currently being used rows in the main table. But at any moment of time, the main table will still have very large number of rows.

Thanks in advance

I already have created Index on those tables.

Yes, but have you created an efficient index? It couldn't hurt to see if some articles might be able to provide some advice. For example:

http://www.databasejournal.com/features/mysql/article.php/1382791/Optimizing-MySQL-Queries-and-Indexes.htm

(Warning: First visit creates an ad - sorry about that - it was just the first hit from Google that looked relevant.)