If some frames are sharp and others are blurry, it’s more likely a shooting/handling issue than film development. The most common cause is camera shake rather than focus.

A good rule of thumb for handheld shooting is to use a shutter speed of at least 1 divided by the focal length of the lens. For example, with a 35mm lens, aim for about 1/50 sec or faster. Slower speeds make blur from hand movement more likely.

Technique also matters: support the camera firmly, avoid jabbing the shutter button, and press it smoothly. A steadier grip and gentler shutter release can make a big difference.

If blur appears only in one section of the roll rather than randomly throughout, lens cleanliness could also be worth checking.

To improve sharpness:

• use faster shutter speeds when handholding
• hold the camera more securely and squeeze the shutter gently
• use a tripod when possible
• open the aperture if you need more light
• check that the lens is clean

Since some images are already fine, your camera is probably basically working, and technique is the first thing to improve.