how do i prick out young tomoto plants to promote new growth

Do you mean prick out as in move young seedlings to a bigger pot?OR pinch out the side shoots so that the plant produces one strong main stem from which it will throw out trusses on which there will be flowers and then tomatoes?

Yes, I did mean how to prick out the leaves/side shoots to promote growth

ok, just pinch out the side shoots that are in the fork of the main stems. This will help the plant concentrate on the main stems for fruit and upward growth.