Well, with any piece I generally start with working to discern the overall form (as best I can anyway). The main reason I do this is because I am VERY much a "context-girl". I completely thrive on discerning a context for any ideas presented to me --in life in general, including music-- and if I am sensing there is something "behind" an "individual" concept I am being presented with, nearly my whole efforts will be diverted to seeking out that
context and then working to discern wherein the individual concept may lay ("individual" concepts become more or less obsolete). As a matter of fact, it is nearly impossible for me to feel like I understand anything without finding it's context.
With that having been said, I firmly view the overall structure of a musical piece as the context for every musical idea within it (something like a frame acts for a photo, painting, or drawing). Since Classical sonatas, including Mozart's, mostly follow a common and known form -- when/if this form is not followed, by knowing the common form, one then has a context for understanding when something is "different" (and how/why) and what effects those differences might have.
I will generally follow the same practice strategy I would use with any piece of music :
1. Number the measures
2. Formal Analysis
3. Find phrases (or otherwise chunks of music that makes sense to me as a chunk)
4. Find repeated material/Roman Numeral Analysis
5. Discern which material is the most complex and work on the most complex sections first
6. Plan out 20 minute sessions, with 10 minute breaks in between (I use a timer)
7. If I cannot play the entire (most difficult) phrase, from memory, w/o mistakes w/in 20 mins. the piece is too difficult.
8. Practice in 20 min sessions.
9. Keep a practice log to keep track of each piece practiced on each day. As well as sections of the piece and what level of competency was achieved during the practice session.
I hope this helps

m1469