I agree with others that 12 months seems early to be concerned. I had some concerns about my twins at various times. At the early age, my pediatrician said that as long as the comprehension is progressing then it's okay.
If you are looking for things you can do at home, here are a few suggestions.
One, is just talk all the time and describe what you are doing. It seems funny to do at times, but just hearing you talk will help. For example, "I'm going to get you some milk. First I need to open the refrigerator. Then I need to grab the milk carton. Now I'm pouring the milk into your cup. Here is your milk." The more you talk, the more exposure the child gets. I had a tough time with this because I don't talk a lot.
Another suggestion is repetition. If, for example, you are playing with a ball with your child, repeat the word ball many times. Examples,"We are playing ball. Do you like the ball? Can you roll the ball?" As your child progresses in speech, you can then expand on it. If your child says ball, you can say "yes it's a ball. It's a blue ball. The ball is round." So you start small and when your child masters that, you add in extra words to describe the object. Don't be surprised if your child doesn't say the full word at once or if it's just a partial word in the beginning. Some sounds are harder than others and take a while (even years) to master.
The third suggestion I will make is to just read books to your child. Point to the pictures and talk about them. My kids tended to like books that had some kind of rhythm and/or repetition.
And a funny speech thing happened at our 4 year check-up. I was a little concerned about one because some of his words were kind of muddy. The pediatrician had him say the words "buttercup" and "silly rabbit" because that tests certain sounds (mouth movements). He couldn't do it so she said I could get him evaluated but it's likely he would pick it up on his own in time. But then when we got home, our nanny asked him to say the words again and he did it better than his brother did. And then he says, "I have to go back to the doctor so I can say buttercup."