So, judging by your answer to my comment you are most likely talking about so-called consumption-induced alcohol tolerance, that one might develop by regular drinking of alcoholic beverages.
We can group the reasons for increased tolerance to the following groups: better adaptation for the elevated concentrations (functional) or increased break-down (metabolic).
This means that your body and its organs, especially your CNS, adapt to compensate for the increased alcohol concentration and manage to sustain its functioning despite the elevated blood alcohol concentrations (BAC). So, the dose of alcohol which previously led to trembling and disorientation now evokes only some coordinatory disturbances.
The physiological mechanisms involved here are:
1. Desensitization of the alcohol-sensitive (primarily GABA-ergic) receptors in CNS.
2. Changes in the neuron firing rates (to compensate for the deterioration of the GABA-ergic inhibition).
This condition is characterized by the increased alcohol break-down by the liver, that slows down the increase of blood alcohol concentration (BAC) upon its consumption leading to the attenuation or complete disguise of alcohol intoxication (inebriation).
The main enzyme that is responsible for alcohol transformation is the so-called alcohol dehydrogenase (ADH), that represents a group of substances catalyzing the alcohol oxidation to aldehydes. This enzymes are located in the liver cells (hepatocytes) and the increase in their activity (and most likely also the absolute amount) is not well understood. It happens, by the way, not only on alcohol consumption: the intake of barbiturates also leads to the increase of ADH and tolerance.
Here you can find much more information about acquired alcohol tolerance, but mostly from the behavioural viewpoint.