Welcome to the Pentax Forums!
Originally posted by jkcerezo Is there a way to utilize the performance of the lens?
What lens should I invest next that's just right in the budget and an all-arounder?
1. The best way to utilize the performance of the lens is to learn to use the camera. If you have the camera manual, that is a good place to start. If you don't, you can download a copy for free from:
Pentax Manuals | Manual Focus
2. Is this your lens: Sicor-XL 35-70mm 1:3.5-4.5 MC ? It is probably a decent tool to get started and to help you learn the basics of how to use your camera.
As for what lens you might want to buy; conventional wisdom is that a non-zoom "normal" lens, a so-called "fast 50" is good to have. I own the Pentax-M 50mm f/1.7 and can heartily recommend it as an excellent option at a reasonable price (~$45 USD) when you are ready for a small and light lens that is good in low light. Your camera was probably sold new with either a Pentax-M 50mm f/1.7 or a Pentax-M 50mm f/1.4.
The film SLR section of this site is a great resource for technical advice as well as information on how to use your camera. I am sure you will be a welcome addition to the crew.
Pentax Film SLR Discussion - PentaxForums.com
Steve