You and your buddy are going to be sharing your lives for years to come so choosing the best forever dog to fit your lifestyle is extremely important.
Some dogs are always on the go and need a lot of exercise, others are couch potatoes. Some shed a lot, but are fluffy and cuddly, some don't shed so much. Some dogs are more easily trainable. Some are very friendly, others are more aloof. Some hate being left alone, others are more independent.
Although most of the dogs in a shelter are probably mixed breeds it can be helpful to research basic dog types to find one that will be best for you. And don't forget to talk to the shelter staff about your needs and ask for their help in matching you and your new buddy.