To be fair, a better lens will *help* you to get better images, but your ability to make the most out of your equipment is what is really going to make any difference in your photos. Just because someone drops down $2200 for a 70-200 f/2.8L IS lens doesn't mean they can't still take poor quality photos. Yes, the 18-55 kit lens and the 55-250 are cheap lenses, and there are certainly better lenses out there. However, my advice to you is instead of spending money on better lenses initially, learn to use what you have. You can see if you really feel like it's worth your while to upgrade from basic hobbiest lenses. -Plus you have a wide focal range to work with, so if you do decide to upgrade your glass in time, you can see what focal lengths you're getting more use out of and find the upgrade that's best for you.
I got by with the 18-55 for some time, and it got me some results I was actually pretty happy with:
IMAGE LINK: http://flic.kr/p/e9SKDM
I still use the 55-250 pretty often, and it's also delivered some decent results:
IMAGE LINK: http://flic.kr/p/knic32
Above all else, just keep practicing. Even trial & error can teach you quite a bit. When I got my XTi, I burned over 400 pictures in that first weekend. I kept maybe a handful. But every photo I took was a learning experience, and by the end of the weekend, I had a much better understanding of how to use my camera. Even then, I still had a lot to learn, and began doing a lot of reading about lighting, exposure, etc. Look into some of the guides other posters have suggested, and POTN is a great resource to have as well. -I've certainly learned a lot from this site and all who contribute to it.