I just got my first dog as an adult 2 weeks ago. We got Sarah, a 3 month Boxer / Golden Retriever mix from a person who couldn't keep her due to health issues.
We had to break a lot of bad habits such as sleeping in bed, eating people food, and drinking sweet tea and Mountain Dew.
So far, we have had pretty good success. She doesn't sleep in our bed now. We have started crate training and have good success with house breaking her.
Sarah seems to still have issues with separation anxiety. She also has issues with inappropriate jumping and trying to nip/bite.
I adopted a two month old cute stray dirty to the hilt and full of fleas puppy. My daughter bathed and treated her and her other two siblings and eliminated the parasites. But training and changing a dogs ways is a time consuming and patient demanding task. So persevere. My dog is about eleven months old now and usually behaves but I have had to be persistent.