Even if you don't have a garden, you can still grow your own vegetables and herbs within your flat. As well as brightening up the place, they have a useful function as opposed to flowers*. Basil's a brilliant plant to start with: it's a hardy plant and has survived a lot of abuse I've subjected it to. It has a lovely aroma and adds a wonderful fresh flavour to your dish. The directions for watering it read 'water when it visibly starts to wilt' and it's fun watching it perk up very quickly after you do. A former basil plant I had actually flowered (former because I killed it by fatally crushing it in a move). I've used basil heavily in dishes such as homemade tomato and basil soup, as well as a garnish in dishes like leek and smoked salmon pasta.

Herbs are easy to grow in pots and seemingly need little care indoors: I've successfully grown parsley and mint as well. If you're conservative about how much you use, taking a bit from multiple pots at the same time, they grow back fairly rapidly. There's quite a lot of relative cheapness compared to having to buy them over and over; they keep on yielding good amounts for little care. I'm not sure about where you live, but I can get them at 'Live Salad' sections in my local UK supermarkets for under a UK pound.

Currently, I'm trying out growing tomato plants, which are growing from little plugs in some compost:

They're apparently meant to scare pigeons away, which is why my roommate agreed to have them. So far, they've not been much trouble, needing only to be watered a bit every day. They grow fairly quickly and need a fairly large pot. We've added some secret plant food, courtesy of roommate parent's, which looks like the blue pill recently. They didn't seem to need that extra care, though. Once they're big enough and the weather's warm, we're going to move them into the balcony to hopefully aid in keeping the pigeons away. I'm looking forward to some fresh tomatoes.

The perfect place for plants seems to be the kitchen windowsill; there should hopefully be plenty of sunshine with a nice room temperature. Be aware that an inevitability with plants is a few small bugs, which is why I wouldn't recommend them in your room. A little method we used to get rid of some rapidly reproducing aphids, which got to the point we couldn't leave them alone (we first tried a ladybug or two, their natural predator, but they couldn't manage them) as they were killing the plant, was to put in a small amount of some washing liquid into water and spray it on the plants. Trying to wash them off with water is another method.

*Edited to Add: Flowers: That's not to say flowers have their own purposes such as aesthetics & beauty or a few special things e.g. rose tea, flytraps.