I would try placing the loveseat perpendicular to the sofa. Since you feel there is a large empty space maybe you could add a sofa table behind it.

Art is always important and I find curtains and area rugs help warm things up and give a room a finished look.

Is the sofa centered to the middle of the television, if not, then center it and move the love seat to make the sofa look like an L shape. The edge of the arms will meet at an angle. The I would look for a large piece of art to put over the sofa which has colors in it that you love to see. From that, you choose one of the colors you like the most and get pillows to compliment the art. Try that for openers and then show us a pic and we can advise more. Here's a picture for inspiration, scroll down on the attached page.... placement

Congratulations on your first apartment. It's very nice and you'll get it looking like you want with just a little time and effort. Look online, google and pinterest, for ideas for low cost art - some even do-it-yourself can look great. I always think going LARGE for art is better than small pieces. It has more impact and looks less cluttered. diy art link

I agree with making an L with the couches. You don't have to have the arms touching - you have plenty of room to play with the placement to see what works; no sense in crowding them together, but you want them close enough that it seems like a cozy conversation area.

It's totally fine to have blank spaces, not everything has to have something filling it. You would have room for a tall piece of furniture facing the entry if you want. Like a china cabinet type piece or a large bookcase. Maybe more than one bookcase if you go that direction, as one might look too puny in that spot. Check on Craigslist - even the free section sometimes has furniture pieces that people haven't been able to sell quickly and they are moving away, etc.

Just for example...this is on my CL for free:

this one is $75 - probably needs a little tlc:

Would start by changing the the angles of sofa, loveseat, and table.

Had the opportunity to work with an interior designer who encouraged putting furniture at an angle, she showed me how many showrooms actually do it.

I did it in a couple of rooms (even dresser in bedroom) and am amazed at how much better things look.