Of all of my friends I'm probably the least interested in interior design, however even I'll admit that staying in a rented apartment can be hard. Having your own space is a blessing, but having limited freedom to do what you want with it can be a challenge. My boyfriend and I have so far rented two flats together, the first of which was something of a wreck and, however much I love the place we're in now, there are still aspects of it that I'd love to change (not least the heavily textured magnolia walls).
In rented accommodation it's important to remember that it's the small details that will make the most difference. Littering the space with bits and pieces that have sentimental meaning is important and the most effective way to really make the house feel your own. Keeping a few pieces from your previous home will keep a sense of familiarity in your new space; as will picking finishing touches that have a special connection to you and those you live with.
One of the most important things I've learnt from renting accommodation is that it's still possible to be creative with the space. More often than not, flats and apartments that we've viewed have had existing tenants living in them, leading to us having a pre-formed idea of the possibilities (and limitations) that the space has to offer. While it's likely that the permanent fixtures and fittings are beyond your control, there's nothing stopping you playing with the furniture inside, even if your accommodation comes ready furnished. In our old flat we experimented with swapping the lounge and the bedroom around, as well as rearranging rooms on a regular basis to keep things feeling fresh.
When it comes to kitting out an unfurnished apartment, I can't sing the praises of second hand furniture enough. Although we eventually splurged on a new sofa, I'm pretty certain that almost everything else we own came from a charity or antique shop. The lack of stability with renting means that we weren't comfortable spending excessive amounts on pieces that may not fit in our next home, plus choosing unique furniture has helped to turn the space into something that truly feels our own.