Apologies for thread necromancy, but the best way to level up is to generally hold off on leveling until you have developed your skills a bit more so that you have more attributes to spend.
Unfortunately, there doesn't seem to be a way to stop the spammed messages about leveling up. These messages are prioritized and repeat endlessly, which blocks any other action that generates text in the top left-hand screen. Nehrim Expanded delays the messages so that they occur often enough to the point where they do not block other actions that generate text in this area.
Of course, you don't have to do this, but it is how Sure AI designed the system. They designed it so you didn't have to plan stats accordingly and could level up more naturally. Assigning levels to quests and areas was supposed to give the player a general idea of where they need to be level-wise to do the dungeons or quests associated with that area, but since you are free to level whenever, the levels become more of a suggestion than an actual requirement.
Some examples include: Exploring Death Pass (Level 26 to 28) around Level 12 or so, doing the arena around Levels 25-30 (against often Level 40 opponents), using followers and summons to help take out higher-level opponents, etc.
Although Sure AI did not eliminate efficient leveling, they incorporate a method to control it more effectively than Oblivion.