Brakes won't stay tight
You need to figure out what's getting loose.  There are essentially 3 possibilities:


The brake pads are wearing down.
An adjustment -- either the twist adjustment, the cable clamp, or the pad itself -- is slipping.
The cable is "stretching".


If the pads are wearing that rapidly, it may be poor quality pads, or you may have some roughness on your rims.  It's also possible that your brakes are dragging all the time, due to improper setup or slightly "tacoed" wheels.

If an adjustment is slipping, you may just need to tighten a clamp tighter, or you may, eg, have an adjuster where the "bumps" that are supposed to hold it in place have worn down.

If a cable is "stretching" it's usually because the cable is breaking, strand by strand, and is in dire need of replacement.