A lord didn't really levy up peasants. Taking an arbitrary time period like 1000-1200 (which happens to be my favorite) most feudal levies would consist of landholders.

Think about it; it takes money to pay for arms and armor, and in the mostly agrarian feudal society, the people with money were landowners. Also, collecting tithes and rents from estates left them with a lot of free time to train to fight.

A really fun popular history of the Normal Conquest is "1066, The Year of the Conquest" by David Howath. In it, Howath goes into detail how the King of England would call his Earls to arms, who would in turn call their respective Thains to arms, each Thain having been granted a tract of land and serfs to work on it, with the obligation to fight for their lord in exchange (Feudalism!). Marginally mentioned by Howath, but given new relevance by recent scholarship, is the presence of Huscarls (or Husjarls, I'm not sure which spelling is more in vogue nowadays) which were servants tied to the household of an Earl or the King charged with the protection of their liege, which we think made up a large portion of the fighting force at Hastings.

Of course, these are very broad strokes I'm painting with. The traditional "Feudal Society" model starts to break down when you start to get into the details, especially when you bring cities into the picture. Some cities, especially in Italy, could have a "Citizen Militia", whereby free citizens where obliged to keep arms in the house should they be called to defend their city. In Venice, lotteries where drawn in times of war; one citizen would be selected for military service, and four others would pay for his equipment. In Milan, seven families were given the obligation to arm the citizenry and organize the defense of one of the city gates in time of war. These families, however, were also large landowners outside of the city, and not only held multiple fortified estates with an ample retinue of Sergeants (or Serjeants; I'm not sure what the most popular spelling is nowadays; they are analogous to the Germanic Huscarls) but also could subdivide their estate into smaller holdings assigned to individual knights (who in exchange, of course, could be called to arms by his liege).

Ooh, can I add some specifics to this?

Let's say we're asking about Henry I of England, in his battles against Robert of Normandy. How were his peasant levies trained for battle?

And compare it to Henry V, after Agincourt. Was peasant training or levies handled differently?

Could you be a little bit more specific? The Middle Ages lasted for a thousand years and were global.

Training for what? Did the lord conscript them for war? If so, as soldiers or as logistics (latrine diggers, supply lines, etc)?