How to identify SMD devices from the codes on top of the component?
KT3 is a BAS21 diode.  Link goes to the data sheet, includes information on similar diodes (BAS19/BAS20/BAS21) and the date code (yours seems to be July 2007)
CVL seems to be a transient voltage suppressor.  The link goes to a site with lots of SMD codes.
A48 could be one of several things.  You'll need to compare the connections of your chip to the datasheets of the various parts that may be marked A48 (most likely a voltage regulator.)
1PX looks like its a voltage detector.


For the 1PX, the dot shows pin 1.  Putting Pin1 at the lower left mean you read it 1PX instead of other combinations you tried (K and stuff.)

Sorry, I can't give you any really good tips for finding the codes.
The linked site helps, and there are others like it, but it all comes down to having good google-fu.
Google, get ideas, check the circuit against the datasheets.