Every garden is located in a climate, and every climate has a name. You might not know what yours is called, but you know things like how cold it gets in winter and when it warms up in spring. As a gardener, you must know these things, because plants are very sensitive to climate. Like snakes and lizards, they cannot regulate their temperature, but unlike those animals, they can't seek shelter from extreme weather.
Temperatures affect viability and performance. Whether a plant will thrive for you is strongly related to its cold tolerance and sun/heat tolerance. Cherries, apples, and pears need cold winters to make fruit (performance). Citrus and avocados will freeze to death or at least lose their crop if it freezes significantly (viability and performance). The amount and form of yearly precipitation is also important to plants, as is its timing. As gardeners, we can make up for inadequate precipitation, and many plants don't mind too much precipitation if the soil they're in drains adequately. Plants available in nurseries and garden centers near you are likely to be suitable for your climate, so you don't have to be an expert when you begin making selections. Of course the same is true if you exchange plants and seeds with your neighbors and friends.
If you're embarking on an outdoor garden for the first time, don't let any bad results you might have had indoors get you down. In a small pot, with only the light available through a window, plants kept indoors are somewhat like inmates of an inadequate institution. Failure to thrive might technically be your fault, but the conditions are set against you.
Still, you might want to keep things simply when it's time to make something of an expanse of bare soil in your hard or community plant, and for that, you can do no better than sow wildflower seeds. You will get a beautiful display out of a few ounces of wildflower seeds. They grow quickly and of sold for your local market, will be tolerant of the weather, no matter what it does. It's all good with wildflower seeds! Most climates will allow wildflowers to grow in spring and summer, they're low maintenance and their good for birds, butterflies and bees.
With a little help from you in the beginning, planting wildflowers will help to suppress weeds. A week or so before you sow your wildflower seeds, start watering the soil to a depth of a few inches. Don't let it dry out completely, and you'll soon see many green spikes poking up through the soil. You must ruthlessly kill them all! They're weeds. (What is a weed? A plant that likes to grow more than people like to grow it.) Pluck away weed seedlings as soon as you recognize them. If you don't, they will bloom and set seed, or spread horizontally with runners or other fancy footwork.
Pay attention to the appearance of the weed seedlings. If you can recognize them you will always be able to eradicate them while preserving the seedings of the plants you want in your garden.
Keep those weeds at bay for a week or so, until the day comes when very few new seedlings appear to replace the ones you killed the day before. Then you may sow your wildflowers. If it's already hot, do it in the evening so they'll have all night to absorb water from the soil and can germinate in good condition when the time comes. It will just be a few days at most, and only a few weeks before something is blooming.
Plunk a few sunflower seeds here and there, considering the height when you choose their places. They are trouble-free, and definitely one of the happiest plants you can grow.