your kit lens is enough for casual shots, there is no need to buy a good lens because you want to shoot better photos. good equips helps to get good photos, but doesnt ensure in getting one. fundamental is still the most important.
indoor shots, most importantly is still lightings. since you have an external flash, try to bounce it off white walls, preferably wall 45 degree behind you, not directly above, so the shadows wont be dark off the chin and under the eyes of your friends. Use biggest aperature ( lowest value F-stop) for solo photos, F4-5.6 for taking several friends, F8 for big groups if you like their face to be sharp. Always try to meter neutral gray colors for explosure consistency, and focus on human eyes for portraits, if eyes are not sharp, nothing else matter.
Shutter keep at 1/focal length, if you want more ambience light, get it lower, the lowest i can go is 1/15, you can try on that, it takes some practice with breathing technique. Iso maintain at 400-800 since you are using 1000D, i wouldnt recommend higher than that.
lastly, i dont agree that kit lens is as good as the 1k lenses, they are good, till when you can tell the sharpness off from a 1k lens, and able to apply your fundamental skills to make the good lenses does wonder, then it justify the price you are paying.