How to get rid of cooking smell in small apartment?
Ventilation, ventilation, ventilation is the only safe way to keep any building smelling good plus dehumidification. You must be sure your range hood is not the recirculating type. ie; If it blows the air back into the space it does not vent outdoors. If it does vent outdoors and does not suck the cooking vapors to the level desired you may need to equalize the pressure by opening a window in another portion of the space to make up the lost air from the ventilation fan. When showering always use the bathroom fan and/or open a window. Fans on timers are always best. Set to 60 minutes after leaving a shower to dry the room out. Dehumidification may be a requirement if fans do not help. This will help maintain low odor thresholds in any home. High humidity above 50% rh (relative humidity) will increase indoor odors and mold growth. To dehumidify you can use window fans and in some cases mechanical dehumidification may be required. (Dehumifier) 
You can review the ASHRAE 62.2 or 62.1 standards for the heating and ventilation industry. Never resort to scented candles or air fresheners as they may release toxins into your living space eventually making you ill.  

https://www.ashrae.org/resources--publications/bookstore/standards-62-1--62-2