You have to make sure you feed them every day and make sure they always have acccess to water. They have to get get excerise and if you don't live somewhere with a big yard you have to walk them pretty much everyday. You also have to housetrain them unless you want them going to the bathroom in the house everywhere. Also make sure you take them to the vet for vaccinations and checkups or if anything seems out of the ordinary. It also helps if they have some sort of chew toy so they don't chew on furniture or anything. I have 3 dogs soo i hope this helps haha :) Good luck!
Having a dog is a BIG responsibility. You need to feed the dog, walk the dog, brush the dog, give him love and compassion. NEVER absue him/her. If you think your dog needs lessons on manners or tricks take them to a local Pet Smart or anywhere else where they give lessons. I have a dog and I love him to pieces!! Even though there a big responsiblity there always there for you! :D
It's like having a baby in the house if you get a young pup. They need to be taken out frequently, often in wee hours or the middle of the night. They need small, frequent meals, companionship and love (to be held and played with), to be walked, to be house and leash trained as well as behavior trained, to be bathed, brushed/groomed regularly. and don't forget regular healthcare as well. It's an immense but rewarding experience.
Vet and vet bills. If your getting a puppy there is always training. For example potty training and teaching it to sit and things like that. Also you have to walk it and take it outside often. Also you should play with it often and give it plenty of attention and love. And there is also the feeding and giving it water. Good luck.
The only thing not mentioned so far is that in many communities, you have to get a license for your dog, which is a little metal tag you put on it's collar, so if it gets lost, the police can help you track it down.