I don't...
I use the rules in the DMG for adventure design; dividing the XP needed to level into encounters, quests, and skill challenges of various difficulty. I fill out those encounters with the intended monsters for the level, and then I stop worrying about XP values and look at the encounter schedule.
If a low difficulty encounter could use another monster, or some minions, I throw them in. If a high difficulty encounter looks like a meat grinder, I look at removing or swapping out monsters. If there are just way to many encounters for the pace I intend for the adventure I remove some or mark them as optional and use them as "random" encounters if the need arises. If there aren't enough encounters to convey the scope of the adventure, I add as many additional encounters as necessary. I do all of this without adjusting the XP values of the adventure. When the party wins the day, they get a level.
I use the rules in the DMG for adventure design; dividing the XP needed to level into encounters, quests, and skill challenges of various difficulty. I fill out those encounters with the intended monsters for the level, and then I stop worrying about XP values and look at the encounter schedule.
If a low difficulty encounter could use another monster, or some minions, I throw them in. If a high difficulty encounter looks like a meat grinder, I look at removing or swapping out monsters. If there are just way to many encounters for the pace I intend for the adventure I remove some or mark them as optional and use them as "random" encounters if the need arises. If there aren't enough encounters to convey the scope of the adventure, I add as many additional encounters as necessary. I do all of this without adjusting the XP values of the adventure. When the party wins the day, they get a level.