Consider your budget when you set up your plan. Do not spend a lot on marketing. There are a lot of tools to promote your products and services for free. If you know the target group on which you need to focus, you end up saving a lot of money, time and effort. Always only direct your promotional efforts on people who will be willing to buy your stuff.
If your products or services are seasonal, that is , relevant only to a certain part of a year, then you will have to time your advertisements accordingly. Promoting stuff for Christmas in March or April is not going to fetch any sales. But it is important to promote during October and November for the holiday season. You might want to promote your products before they are available to public. However, it is not a great idea to make your customers wait for long as they might lose interest in what you are trying to sell.