The first thing to decide is that you really want a garden of your own, and mean to work in it and keep it clean and tidy. The next thing is to learn a little about situation and soil, because you cannot choose which plants to grow until you know what conditions you can give them. You must not think that you can ram any plants into any patch of ground with success. There are a few that are obliging and will live almost anywhere, but even these will generally show you by their size and health whether they like their home or not. Many will just exist, but not do well without the food or place that suits them, while others will die unless they have what they want.