@alora If you want to re-inspire your dog to obey your commands and do so without thinking about it first, use a high value treat.
Keep your treats in a small hard plastic container in your pocket and be generous. If he does a good sit or obeys well, give one treat after the other (dogs perceive this as higher value than one large treat).
Fading out treats should be done once the dog is really solid with commands.
Use commands that you are comfortable with but honestly if you want your dog to sit, and your language is English, use the most appropriate word.
To get the dogs focus say the dogs name and then the command. Eg "Fido - SIT!" Say it only once and mean it. Give the dog time to obey and then reward highly.
If you think the dog is confused about what you mean, go over the initial training of that command to make sure you are both on the same page and please seriously consider a 'marker word' or a clicker. Going over training steps is necessary from time to time and can be quite valuable to help a dog get what you are wanting.
Marker words are so valuable with training. I use (Yes!) but you can use whatever word you like so long as you are consistent and follow through with the rewards. You need to load the marker word first (do the research) and be consistent with providing the treat following it's use. This will help the dog understand what you want, what will happen if he obeys (treats and praise) and is useful when training more complex tasks.
Research and try out other delicious treats to get your dogs interest and focus on training and rotate them in and out of use. Dogs do get bored of the same old, same old.