econimy picking is basically putting together alternate picking, and sweep picking together. you always pick towards the string you want to play. this means that you willl not nessasarily play strict UDUDUD but might play UDUDDDUDUU. or somtheing like that

for example you would play the following riff

...D U D U .U U U D U. D U U D U .D .U
--9-7-5-7------------------------------
-----------6-----------------------------
-------------5--------9-----8-------------
---------------7-8-10---------7-10-8-----
------------------------7------------------
--------------------------8-----------------

made that up on spot without lookin at guitar so probably sounds horible but hey, its an example. it means that you have to move the pick less as you always take the quikest path to the next string. the only thing to be carefull with is it is harder to keep a good rythm (in my opinion) with econimy picking, people tend to rush the swept bits. but yeh a very good thing to master, which will also open up sweeping muchh more to you as i wont feel like switchin between seperate techniques.