- Tune those queries. Biggest bang for your buck. Enable the slow query log and watch it. Once you've found a heavy resource intensive query, optimize it! Tune what receives real-world traffic.
- Employ Master-Master Replication. Immediately have a read-only slave for your application to hit as well.
- Use Your Memory. Set innodb_buffer_pool_size, key_buffer_size and other key options.
- RAID Your Disk I/O. Use RAID 10 mirroring and striping. On EC2 striping across a number of EBS volumes using the Linux md software raid.
- Tune Key Parameters. speeds up inserts & updates with innodb_flush_log_at_trx_commit=2; create a tablespace and underlying datafile for each table with innodb_file_per_table.
Full details at the original article.