Every trainer has their own philosophy around whether or not pets should be allowed on the furniture or not. I am a little more laid back. I believe that you should be allowed to let your dog up on the couch or bed if you want to - I just try to encourage some healthy furniture rules.
1. Must be potty trained
This one may seem a little straight forward, but a lot of people just can't wait for their dog to sleep in bed with them! If your puppy (or new dog of any age) is not potty trained and you let them sleep in bed with you there is a fairly good chance that you will wake up to an accident or two on your bed. Now you may be thinking - you are only talking about the bed, so the couch or a chair should be fine! What most people fail to realize is that dogs (in general at all ages) do not have the ability to generalize, so if they are allowed up on the couch, they may see the bed as free game as well. My recommendation is to wait until they are fully house trained - no more accidents in the house - or, even better, until they are over 1 year old.
2. Only when invited
Furniture privileges should be your decision, not your dog's. Your dog should have somewhere to relax around the furniture that is their own space. Have a blanket or a bed and train your dog that that is their area to lay down and relax in. That way they can chill out with you in the same room without being in your space. When you are ready for a couch or bed buddy, invite them up.
3. Not allowed to beg
If they are standing and staring at you with those powerful puppy dog eyes and willing you to let them up on the furniture, don't do it! Like the above point, it is your choice when they get to be on the furniture. Begging for couch time is like begging for food - a bad behavior. Reinforce that they can relax in their own spot (bed or mat) until they are invited up. This doesn't mean that they need to be on the furniture every day. If your dog is having a naughty day, don't let them on the couch - especially if it is something that they love!
4. Must sill lay on their bed (or sleep in kennel) when asked to
We always want to reinforce that they have their own area. Sometimes we need our space from our dogs - not that they always understand that. Make sure that you work on a really good "on your bed" command in order to be able to send them back to their chill spot if they are begging for couch time. My dogs will occasionally get a night in bed with us, but other nights they sleep in their kennels. A lot of times, if you have nights in bed outweighing nights in the kennel, your dog will begin to hate going to their kennel. Keeping a healthy balance of furniture allowance to their own bed or kennel time is important.