After you can do that stuff using "alternate picking" then try doing runs where you skip strings in between phrases and/or notes.


e |-----------------------------------------------------------------
b |-----------------------------------------------------------------
g |-----------------------------------------4--3--2--1--------------
d |---------------1--2--3--4---------------------------------------
a |----------------------------4--3--2--1---------------------------
e |--1--2--3--4----------------------------------------------------

or


e |---------------------4-------------------------------------------
b |---------------2--------3--4-----2-------------------------------
g |----------4-------3-----------------3----------------------------
d |-----2-------1----------------1-----------3----------------------
a |--------3------------------------------4-------------------------
e |--1-------------------------------------------------------------