By loving the other person more than you love yourself. When you want to criticize ask yourself these questions:
Is it necessary.
Is it kind.
Will it do any good.
If the answer is no to any of these, either rephrase or SHUT UP. Time and the working through of your differences - with LOVE and PATIENCE and the knowledge that no relationship is perfect and no person is perfect- will OVER TIME create a strong, long lasting relationship. If you haven't got the patience for a long, difficult haul...maybe you aren't meant for serious, rich relationships.It's a heck of a lot of work and compromise. It IS worth it however...