First of all, it is very important to look after your tools and keep them maintained - well-kept and well-serviced tools run smoothly and with minimal vibration.
Random orbital sanders are designed to be used with specific sized pads, with a precise weight. Make sure you are using the correct size pad, and that it is in good condition.
Change your backing pad regularly - large chunks of missing pad material will cause imbalance.
For some product ranges, Mirka also offers the myMirka app with a vibration sensor, which helps you monitor vibration levels during working.