If this is your first year gardening, take it slow. Plant a few tomatoes and peppers. A small herb garden. Some beans and lettuce. Maybe some onions. Get used to how certain plants grow and their needs.
Do you love fresh tomatoes and tomato sauce? Is salsa your thing? Then tomatoes should definitely be on your to-grow list. Are potatoes detested by the entire family? You might want to skip them.
You can usually get by with somewhat smaller spacing than seed packets tell you, but make sure that each plant has ample nutrients and sun. You can also use vertical gardening techniques to conserve space.
It is helpful to become familiar with what certain plants look like as seedlings- so that you can pull the weeds and not the plants.
Your soil is the most important part of your garden- poor soil will not produce much more than unhealthy plants. Before starting your garden each year make sure you amend the soil with well-rotted manure or compost.