I've been playing since last June and have used nothing but the starter equipment until a couple of weeks ago. I finally picked up a new club - The WGT Tour Pro 9.5 Driver. It adds about 20 yards in distance and has taken about a stroke and half off my average. It's also made the game much more enjoyable. You don't have to necessarily get this club, but I would recommend a Driver for your 1st upgrade that's at least 20 yds longer than the starter driver.
Putting is key to this game, but I wouldn't be too quick to get a new putter right away. My putting stats are actually pretty good - 95% 1 or 2 putts and 5% 3 putts or more and I've used nothing but the starter putter. The key to my putting was finding a thread about 2 weeks after I started playing written buy one of the best players on here, Nivlac. It really helped me and many others. In fact WGT has it under the FAQ's "Putting Tips" ------------------------------------------->
Read it and I can just about guarantee that your putting will improve. As noted, putting is key, but if you can't reach the greens in regulation, what's the point...lol.
Good Luck.