Legato is as much a state of mind as it is just the mechanical connecting of one note with the other with your fingertips. The first step towards a true legato is learning to think legato; to think in long notes. Pianists tend to have the bad habit of hearing, and thinking, everything in staccato. We play the note, and then forget about it. As you try to play something legato, it is very important to make a mental connection with the sound and the transition between both notes or chords. By listening carefully to the particular way in which two things connect, we learn to reproduce it and to follow it when we play.
You can smear one note into the next all you want, and it won't sound legato if you aren't singing in your head; if you aren't listening. On the other hand, you can take a pencil and play each note in the phrase with the pencil tip, but if you are listening to the way the notes should connect, it will sound legato,