Well, what are you practicing now, and what are you having trouble with?
The basic alternate picking drill would be a 4-note-per-string chromatic run:
|-----------------------------------------1-2-3-4-|
|---------------------------------1-2-3-4---------|
|-------------------------1-2-3-4-----------------|
|-----------------1-2-3-4-------------------------|
|---------1-2-3-4---------------------------------|
|-1-2-3-4-----------------------------------------|
Walk that up and down the neck, starting slow and building speed. Definitely use a metronome, or a drum track, or SOMETHING to force you to stay rhythmically even.
Lately, I've never been happy with my picking across strings, so I've been practicing variations of this:
Bmadd9
|-------------------------------------------|
|-------------------------------------------|
|----------------------7-7-7----------------|
|-------------11-11-11-------11-11-11-------|
|-------9-9-9-------------------------9-9-9-|
|-7-7-7-------------------------------------|
Dadd9
|-------------------------------------------------------|
|-------------------------------------------------------|
|----------------------------11-11-11-------------------|
|-------------------14-14-14----------14-14-14----------|
|----------12-12-12----------------------------12-12-12-|
|-10-10-10----------------------------------------------|
....and just kind of move it around to other chords in key. I.e, Bmadd9-Aadd9-Gadd9-Dadd9-Bmadd9 or whatever. Do it as one note a string, two notes a string, three notes a string (as written), four, etc. It'll sound and feel a bit different, and the mechanics of changing strings with an even number of pickstrokes per string vs an odd number are totally different (i.e - on this example, you change from the E string to the A string on an upstroke, the A to the D on a downstroke, etc, while with 2 notes per string you're changing with a downstroke every time).
Sit down, think about where you're technique is holding you back, and really
think about how you can design drills to challenge those weaknesses. Then, practice.