Originally posted by barladeanca is there a way to focus on one spot of your choice? Is it possible to focus on a spot and then move the camera to compose?
Yes. You can check the manual or download a pdf version of the manual. i don't have that specific model, but on my DSLR you have to press Info and there there is an icon with some green squares where you can choose Auto point selection (not most reliable, this is for beginners), centre point (this one is fast and reliable, but only uses the centre point, in the middle of the frame), or select point (probably best choice. After some practice, you can adjust which focus point you want the camera to use really quickly)
I would also suggest you go into camera Menu and find the "AF / AE-L button" option (or something similar). Here you can choose which button on the camera will trigger AF. This is great, because you can de-couple the AF from the shutter. Now you can take focus, and move the camera and press as many photos as you want, without the camera trying to refocus. Lots of us have done this, so the AE-L button on the back is the AF button.
Next thing you can do is use LiveView. This uses different AF method, which has its pros and cons (you can google Phase detect AF vs. Contrast detect AF). In live view, you can also go to Menu and enable Focus Peaking. This is a great aide for acquiring focus. In fact, you can switch camera to MF and use manual focus with focus peaking. After practice, you can manually focus faster/better than the AF (though, this depends on the scene as well as the lens)
Originally posted by barladeanca I have the standard 18-50 lens.
This is a fine lens, but it is far from the best in the lineup. Check your photos to see which focal length you use the most, or at least which one gives you the best photos. Then I would suggest you buy a fixed focal length lens (this means no zoom, but much better image quality). Pentax makes great DA 35mm f2.4 and DA 50mm f1.8 lenses, which are really affordable and give you much better image quality and low light performance, fast AF than the kit lens. You can try something like Pentax 16-50mm or the more affordable Tamron 17-50mm f2.8 lens (read here:
https://www.pentaxforums.com/reviews/pentax-16-50-vs-sigma-tamron-17-50mm/introduction.html). These still give you a zoom range, and allow a brighter image, and still have a better image quality than the kit lens. The kit lens is just.. well, the lens that comes with all cameras. By definition it won't be the most top notch technology.
One more thing. Photos can be blurry due to misfocusing or handshake blur (in combination with slow shutter speeds). Misfocusing can happen due to camera making a different choice than what you wanted, or due to user error, or due to lens and camera being miscalibrated. If you are certain the first two options are not the cause, you can try adjusting the AF (there is a camera option for this, many threads and blog posts about techniques that help you do this, including focus charts).
Edit: Also, do not forget the importance of light. I assume the subject are indoors, which usually means dim light. You can light up the room, use a diffused flash, or something else to help you, but this takes a lot of work. And don't forget to adjust the WB to Tungsten or whatever light quality you are dealing with.
And if you shoot jpeg, switch to Portrait mode. Practice practice practice is crucial, as well.