Blurry Photos with the 18-55mm lens?

I'm a beginner Photographer,
I have Nikon D3100 and was doing indoor portraits with 18-55mm lens and A speedlite mounted on the hotshoe of the camera, The lightning condition inside the room was dark so i bumped up the power of the speed lite, they looked pretty good on the camera but when i viewed them on my desktop they were a little bit blurry. They didn't have much clarity as much as my 55-200mm has. What am i doing wrong here

Blurry photos are down to a number of things;
- the camera mis-focusing & choosing the wrong focus point (solution: use single point focus to be sure)
- too slow a shutter speed for handholding the camera or stopping motion blur in your subject (solution: increase shutter speed)
- the blur isn't 'blur' as such but out of focus portions of your image due to too shallow a depth of field (solution: stop down the aperture a bit).