If you are starting a garden project of some sort for the first time, there are a few things you may want to consider well before you start!
Dream Big, Start Small - Having dreams of a beautiful English garden in your back yard is wonderful, but, when you are just starting out--start small. Maybe even start in pots so that if it turns out you love the look of a garden (but not the upkeep) you can get rid of your experiment! Each year you can expand your garden or area and see what works and what doesn't for you. Think about what you love. Would you rather have flowers everywhere or a small vegetable or herb garden? Once you know what you want, read up and find out about what you want to grow--so you can choose the right plants.
Plan Ahead - Now you know the size of your garden and what you would like to plant, you need to see what plants will work in your 'zone'. Different areas of the U.S. are divided into different planting zones and they are numbered. So before you can get outside, look up what plants you like and find out if they are zoned for your area. (Google is an awesome gardening tool). Also, there may be a time of year some plants work better than others too. Usually (not always) local places that sell plants have several varieties that will work in your zone. You can mail order plants, too, but sometimes those can be more expensive.
Know Your Yard - You have your ideas. You are going to start small. You know what plants you want. Now, you need to know your yard if you are planting in the ground and not in a container of some sort. Is there shade or sun where you will be planting? What type of soil is in the area and how much moisture does it get? These all factor in with your plant choices as well. Some herbs require lots and lots of direct sun, some flowers need a lot of sun, but also shade. Some plants like moist ground, while others like to dry out a bit. If you know your yard/soil/sun exposure it will make your plant choices better and help ease you toward success.
Relinquish Control - After all of your planning and hard work, sometimes the weather or a hungry critter can ruin even the strongest of plants. Gardening can be a bit of a gamble. I have had a container herb garden off and on for years and I experiment with different plants (at least 1 or 2) every year. Some work...some don't. It can be disappointing when something doesn't go the way you expect, but, mostly it's a joy to watch something grow and change! I just figure next year we'll try something different! I have over planted and regretted it and under planted and wished I had more of this plant or that plant, but, mostly it has been something that makes me feel happy when I see all the changes through the growing season. So just let go and see what Mother Nature teaches you when you start your garden adventure!