Do you have, or are planning to have children? If so what are their ages? Do you have a secure garden? Can you afford a dog? Think about the initial purchase costs, plus things like insurance (essential), feed, collar, coats, grooming for certain breeds, holiday arrangements (as expensive as another person going on holiday at peak times at popular kennels). What are your working arrangements? If you both work full time out of the home, it's really not a runner, unless you live very close by or have someone who is willing to help you out every day, or are willing to shell out lots of money for a professional dog walker.
One of the best ways to get experience is to go along to your local dogs home/rescue centre and offer to help out with dog walking. Make sure you do this at regular times every week, in all weathers, fine or foul. Not only will you be learning about dogs and their behaviour, but the commitment will be an excellent way of assessing your JOINT commitment - can't stress that enough. Every adult in the house should be equally signed up to the commitment of dog ownership, if not it will be unfair on you and the dog.
Think about your lifestyle. If you are a design conscious person with white sofas, who likes spending weekends in Barcelona, going out a lot in gorgeous clothes then a dog probably won't fit with your lifestyle. If you don't mind mud, hair, oomska, if you are happy wearing wellies, enjoy being outdoors, and are willing to give possibly around 15 years to making a home for a creature who will be your best friend, as well as drive you potty at times. There's a lot more housework with a dog, and they will often take over your furniture. When they die, which always happens too soon, you will feel a grief that will shred you for years.
Also go along to local "fun" dog shows - just google companion dog shows in your area, or look at the websites for your local rescue charities. Most of these will often run things like fun shows (classes for best rescue dog, waggiest tail etc) or have other social events or meet 'n' greets. These are great, as you can have fun and talk to people about their dogs. Also find out if you have a good vet near you, and if there are obedience classes nearby.
Think realistically about allergies - and the size/temperament of the dog. do you have a car? If so is it suitable for dog transport?
Also, you are in the right place here, as once you start to have specific questions there are lots of people here who will be able to help. The above is not everything but will do to get you started. 