Don't try to grow anything from seed right away - it's hit-or-miss a lot of the time, which can be off-putting. Wait until you've truly understood that, with plants, you're never totally in charge - they are!
Start small - a little patch in the garden, maybe a pot or two. (Bear in mind that pots need a lot more care than open soil - the watering alone is ghastly so you have to be up for it or watch your plants shrivel!).
Don't fill all your available space for the first couple of years. You don't want to lose a lot of plants all at once - for one thing, it's expensive and, for another, you risk feeling defeated. The odd failed pot is OK - a garden full of failures takes very broad shoulders to bear.
Look around a garden centre or two and note which plants they have most of - these tend to be easier to care for and therefore popular and therefore they can sell a lot of them.
Don't buy huge showy plants and don't buy tiny ones. You want ones that have clearly survived their baby days and are now robust teenagers. As soon as you get them, transfer them into slightly larger pots with fresh compost. Once they've grow a bit more, plant them into their final growing position.
Join a gardening club - gardeners just love to help each other out and, as a novice, you're bound to be taken under someone's wing.
Good luck.
