How often should I change the mop head? 

Depends on the floor soil level, area covered and cleaning frequency. As a general rule of thumb for households, every 3 to 6 months or when the mop cleaning effectiveness is noticeably reduced or appear worn out whichever earlier.

For sensitive areas where prevention of cross -contamination is desired or necessary, it is advisable to have separate mop heads (& sometimes mop handles &/or mop sets) for the different areas.

By caring for your mop set and replacing your mop heads regularly, it will maintain its long term effectiveness keeping your home and office hygienically clean and safe from germs. 

The mop head seems a bit draggy when I mop the floor. Am I doing it right? 

Firstly, ensure the mop head is sufficiently spun dry free of excess water with its high speed spinning capability.

The Microfiber mop head being Microfiber material actually picks up dirt and grime without needing too much force exertion (unlike traditional cotton mop heads) in order to achieve the superior shine cleaning effect.

The slight resistance comes from the Microfiber material actually doing its cleaning job. A slightly different but more effective way of cleaning. 

Which is more effective, a mop head or a mop pad? 

Many people forget that a mop is not a broom & large debris/objects on the floor can always be pickup up by a mop. Whilst this is possible, it is always better to sweep or vacuum the floor beforehand particularly if there are large debris present before mopping for that final cleaning, disinfection & shine. Otherwise you risk just pushing the larger floor debris around.

That said, a mop head has much more tufting material than a mop pad which technically means its larger cleaning surface overall allows a greater chance to lift & trap dirt & grime effectively, including larger floor debris. A mop pad would be fine if the floor is relatively clean & clear of debris.