Before dealing with any bad odours the first step is to identify the source. This is an important step as you won't be able to prevent nasty smells from returning, if you don't know where they are coming from. Here are some tips for 3 most common sources:
Drains
Kitchens and bathroom sinks produce some of the worst smells, especially if not well maintained. This is because of the build up of food, soap, grease and grime that attracts bacteria. So make sure you clean and unblock them regularly. You can buy products that do just that or you can do it a much cheaper and eco friendly way, where you use baking soda and vinegar to do the job.
Bins
Your kitchen bin needs to be emptied regularly into your outdoor bin. Smells from the bin is due to the decomposition of what you have thrown away which produces gases and chemicals. The longer you leave it the worse smells will get. As well as disposing rubbish regularly it's important to regularly clean out the bin itself. Cleaning and disinfecting your bin not just gets rid of nasty odours but also gets rid of harmful bacteria. Lemon scented products tend to be best for cleaning them out and also adding a bit of baking soda helps to absorb smells.