One thing that has majorly helped me with gardening is to make a layout before I plant.
It helps you to get a visual of what you will be doing.
It helps determine how many plants you will need to buy or start from seed, therefore avoiding over planting or over purchasing.
By laying it all out you can also determine which plants will go where; in relation to watering schedules, sun location, height in relation to other plants, which plants do well planted together, and proper plant spacing. It also helps when thinking about when to plant.
It is also good to keep if you are in a permanent location that you will be using for several years. For example, broccoli (and other related vegetables) are not supposed to be planted in the same area for at least 3 years to avoid disease.
Making a garden layout is the first thing I do at the beginning of the season, and it is included in my garden journal so I have a copy of it for each year.
I find that it really helps me maximize my space, as well.