It used to be fairly simple to select and install a dimmer for home lighting but it is now a little more complicated with the very common use of LED and Compact Fluorescent lighting. Making the wrong compatibility choices can result in flickering lights or/and a poor dimming range of adjustment Under sizing a dimmer mean it will not last long. Trying to dim lamps that are not designed to be dimmed will simply not work. There are also complications to consider with any two way switching of the lights.
Careful planning is also needed if you have a dimmer already installed on filament/Halogen lamps but wish to change to LED lamps. Typically this would be a swap from Halogen GU10 to GU10 LED direct replacement lamps in kitchen down lighters. Not only will the LED lamps need to be of a dimmable type but the dimmer needs to be compatible with the new lamps.
A good electrician will be able to design and install a reliable solution that best suits the requirement and budget.