In D&D in general, you are more likely to encounter less powerful monsters than higher powered ones. This is a reflection, in part, of the typical food web pyramid used in biology. Food web or food chain hierarchies show that stable ecosystem follow the same pattern in which producers and small herbivores far outnumber top-level predators. There are reasons such a hierarchy may not exist in a D&D world, but let us assume, for the purpose of this activity, that this is generally true for D&D monsters as well as lions, gazelles, and grass in Africa. Even if you don't buy the biology argument, you can, no doubt, see the value of creating such a table for epigenetic character progression. There are ways to represent this likelihood in a D&D encounter table by which adventurers and dungeon crawlers are far less likely to encounter a red dragon rather than a kobold, many of which my readers are, no doubt, passably if not intimately familiar. In this post I share my own method.
Line 'Em Up
The first step is to create a way in which monsters can be consistently and objectively ranked and categorized by difficulty. Hit Dice is one such way, but, for me, fails to take into account important monsters characteristics. To that end I have created my own method for determining relative monster difficulty, which I then equate to experience. My Constant Readers may very easily use their own ranking method and progress to the next step.
The Next Step
After ordering the monsters by power, distribute them around the median of a dice roll outcomes range in which more than one of the same die is used. Doing this creates a table in which monster power is correlated with its likelihood of encounter.