Make sure that you set some time aside a couple of times each week to spend (child-free) with your wife/partner. When your baby is asleep is best. Make it your time to sit and chat or do whatever you used to do before baby came along. Stick to this as often as you can, despite tiredness or being busy. If baby wakes up or you really can't keep the time available, plan for another definite time as soon as you can. Ensure that you maintain a one on one relationship with your partner.
Try to keep some of your regular things happening after the baby is born. If you and your wife used to go to the movies every Saturday night, you could book a regular baby sitter and keep going. If you wish to take baby with you, go to an afternoon session and find a cinema that has a baby room or crying room in it (some do nowadays). You may need to wait until baby is a couple of months old before re-establishing your routine. If you used to do something that you can't take the baby to, try using a baby sitter or change to another activity. The important thing is that you are doing something that doesn't revolve purely around baby.