There are a few practical things you can try, but the main limitation is the phone itself: it uses contrast-detect autofocus, which is generally less reliable and slower than dedicated camera systems.

To help it focus better:

• Aim the focus area at something with clear contrast or edges rather than a flat, low-detail surface.
• Give the camera more light. Autofocus usually works better in brighter scenes.
• In low light, adding a small external light source can help the camera find focus.

Beyond that, there usually isn’t much you can do through mods or software to meaningfully improve the hardware’s focusing performance. So the best improvements come from technique: use better lighting and focus on high-contrast parts of the subject whenever possible.