How do I get my UI to look like that? I'm going to start playing WoW again in about 3 and a half weeks, after my exams finish, and any help would be appreciated.
There's lots of different mods in that picture. Your best bet if you're not very good with that sort of thing is to find a pre-made complation. Search at World of Warcraft Addons | World of Warcraft @ Curse.com or WoWInterface or just use Google.
If you want specific names from that screenshot, I can help with a few.
The bar at the top is FuBar with many plugins. The unit frames look like ag_unitFrames or Pitball (I'd say ag but Pitball will do the same things). KTM Theat Meter is the small black box on the left. XRaidStatus the small box on the right. The minimap is Squeenix or SimpleMiniMap. The main tank frames are oRa2 or similiar. The big box at the bottom with the action bars and chat in it was made with eePanels. The action bars themselves probably BarTender or similiar. The trinket buttons are TrinketMenu. The chat is customized with Prat.