For the purposes of this Diablo 3 Monk leveling guide, we can simplify your skill choices pretty easily. Crippling Strike, Lashing Tail Kick, Breath of Heaven, and Dashing Strike are your essential moves at lower levels. Crippling Strike lets you plow through packs of enemies quite easily.
While it lacks single target damage, you spend by far more time fighting packs of weaker enemies than you do against boss enemies, so you will be better off rolling with Crippling Strike over any other spell. Lashing Tail Kick is a strong Spirit Spender that does good damage to both single targets and groups of enemies. Breath of Heaven heals you and Dashing Strike is a key mobility skill.
Between these 4 skills, you have your key requirements recovered. After this, the final two abilities are personal preference. You will want to pick up a Mantra of some sort. If you are playing a defensive role, you might add on more Spirit generators to get access to multiple buffs. If you are playing in solo you might add on Seven-Sided Strike to make up for your otherwise poor single-target damage capabilities. The choice is yours.
For PvP and special encounters, you will get a lot of use out of other Monk skills, but in my opinion these 4 abilities are your core skills for general Monk play and if you are trying to level up, it is the recommendation of this Diablo 3 Monk leveling guide to include these 4 abilities.
While these 4 skills are core Monk abilities, you will find that there is a lot of variation available to the Monk in your choice of passive skills. Check out our Diablo 3 Monk Passive Skills list for more details on choices for passive skills.