Did you know this about dog training?  

This is a huge loaded question and would take much longer to respond that a few paragraphs.
Yes, I am training my dog. She is almost two.
I have heard that dogs retain everything that they have learned in their first year.
Unfortunately I got my dog when she was fifteen months old.
I believe that dogs are never too old to learn new things.
I started off with my dog by just going about my business around home, with her and out for a walk with her with basic expectations.
I taught my dog to stop before crossing the street and I accomplished this with cookies. Which are actually her kibble. It works now all the time, with or without the cookies, no problem.
I just say stay when we get to a cross walk to look both ways before proceeding,
It helps a lot to learn how to read your dog. To try and figure out the best way that they will understand your interpretation of what you are asking of them.
Not all tactics in training will work on all dogs. Just because Dog A gets it, doesn't mean Dog B is going to so we need to try different tactics in training our dog. What works for one may not work the same for another.
My dog had to overcome some neglect and abuse issues, or repercussions therefrom rather. Starting with confidence in herself and in me as her handler.
This took time and something we continue to work on.
The internet is a great place to learn handling and training tips.
YouTube has some awesome videos. I have learned a lot from that site. So has my dog.
You have taught your dog sit and down, good for you two. You can accomplish more.
Persistance and patience is the key.
Have a plan and stick to it.
I have learned to never feed first and then exercise, to exercise, discipline and reward, in that order for a well rounded dog.
Exercise by a walk, discipline by throwing a ball or stick and have them fetch it, reward with verbal praise when returning with the stick or ball but the real reward is a nice bowl of food when they get home.
I have learned to expect my dog to hold a stay position for a minimum of 30 minutes a day.
This will mean waiting in a sit stay position while I prepare her food dish, holding a stay until I am ready to go for a walk with her. Hold stay in the park as I walk out 20 feet from her and back again. This is a great exercise.
There is so much we can teach our dogs that they are so eagar and willing to learn. We just need to find the best way interpret to our dogs what we are expecting of them. When they understand they will be more than happy to do what you say, in a kind way but firm.
When you walk your dog, stand tall, chest out and be strong and assertive. Your dog will pick up your energy through the leash. Do not look down at the dog as you walk, feel them through the leash and walk forward.
Those are a few basics that have proved to be helpful for us.
At night my dog would bark and bark when we would walk. I have taught her, it's okay and leave it. She knows what it means and it dos work, most of the time. Still working on it,. I find that f I sing in a medium high pitch (she loves choir music) she seems more relaxed during our evening walks.
My dog is training to receive her certificate from citizen canine where she gets her good canine good neighbor reward. http://www.citizencanine.org.
There are twelve tests that she must pass.
What is great about this site is that it shows the twelve tests and what will make her fail. As well as if she fails, the ways I can correct her in training further. Magnificent. Check it out. A great place to start.
You could Google your area and citizen canine to see if there is an area close to you that offers this certificate training.
Basically it promotes responsible ownership but also a dog with good manners in public.
Cheers.