If your stove burns with a yellow flame, it means you are burning liquid fuel. A blue flame means you are burning vaporized fuel, which is hotter and cleaner. On a liquid fuel stove, a yellow flame usually means the stove is not heated up sufficiently to turn the fuel into vapor. Turn the stove down low to allow it to slowly warm the fuel, then turn it up once the flame burns blue. If your blended fuel stove is burning yellow, the fuel canister needs to be warmed.
Most stoves require some sort of periodic maintenance.
Read the stove's instruction manual then save it so you can refer back to it once a year to make sure you are keeping it in top condition. Avoid overheating the stove's fuel tank. Using an oversize pot on a backpacking stove is the easiest way to overheat your stove. Feel the fuel tank occasionally. On gas stoves, tanks must be warm to generate pressure.