Alright, if you don't want to read through this explanation, scroll down, my tab for Step Up is down there a bit. However, I feel it is necessary to explain something about Linkin Park's bass tuning. I see a lot of people
submitting bass tabs for LP songs in standard tuning, drop D, or C#ADG. These tunings are WRONG, plain and simple.
Phoenix mainly uses drop D, half step down for his tuning. That's C#G#C#F#. There are exceptions, but that's his
primary tuning. So to all the people submitting tabs in other tunings, retune your bass and try again. For quick
reference, here's a guide to LP's bass tunings on various songs:

Hybrid Theory:
Papercut - C# G# C# F#
One Step Closer - C# G# C# F#
With You - B E A D G (Standard 5 string)
Points of Authority - C# G# C# F#
Crawling - C# G# C# F#
Runaway - B E A D G (Standard 5 String)
By Myself - C# G# C# F#
In the End - B E A D G (Standard 5 String)
A Place for My Head - Eb Ab Db Gb (Half Step Down)
Forgotten - Eb Ab Db Gb (Half Step Down)
Pushing Me Away - C# G# C# F#

Meteora:
Don't Stay - B E A D G (Standard 5 String)
Somewhere I Belong - Bb Eb Ab Db Gb (5 String Half Step Down)
Lying from You - C# G# C# F#
Hit the Floor - C# G# C# F#
Easier to Run - (Bb Eb Ab Db Gb (5 String Half Step Down)
Faint - C# G# C# F#
Figure.09 - C# G# C# F#
Breaking the Habit - B E A D G (Standard 5 String)
From the Inside - C# G# C# F#
Nobody's Listening - B E A D G (Standard 5 String)
Session - C# G# C# F#
Numb - C# G# C# F#

Other Songs:
My December - C G C F (Drop D, Full Step Down)
My December (Live) - C# G# C# F#
Carousel - C# G# C# F#
Step Up - C# G# C# F#
And One - C# G# C# F#
High Voltage - C# G# C# F#
Part of Me - C# G# C# F#
A.06 - C# G# C# F#
Dedicated - C# G# C# F#
Sold My Soul to Yo Mama - C# G# C# F#
It's Goin' Down - B E A D G (Standard 5 String)
--------------------------------------------------------

Now, on to the actual Step Up tab. The only thing I'm unsure of is the verses: the notes on the 2nd string might actually be on the 4th string, but it's just an octave difference, so play whichever sounds better to you.

~ = Let ring

Verse 1: (No bass until 0:27)
F#|----------------------------------------------------------------------------|
C#|----7--7-7----7-7-5-8--7--7-7--------------8--7--7-7----7-7-5-8--7--7-7-----|
G#|-7--------------------------------------------------------------------------|
C#|----------------------------------------------------------------------------|

Chorus: (0:45)
F#|-------------------------------------------------------------------------------|
C#|-------------------------------------------------------------------------------|
G#|----------8-8-8-7---5-5-5-5---------------------8-8-8-7------------------------|
C#|-7-7-7-7---------------------5-5-5-5---7-7-7-7------------8-8-8-8--10-10-10-10-|

Verse 2: (Starts at 0:56, bass enters at 1:07)
F#|-------------------------------------------------------------------------|
C#|-7-7----7-7-5-8--7--7-7----7-7-5-8--7--7-7----7-7-5-8--7--7-7----7-7-5-8-|
G#|-------------------------------------------------------------------------|
C#|-------------------------------------------------------------------------|

Pre-Chorus: (1:25)
F#|--------------------------------------------------|
C#|--------------------------------------------------|
G#|--------------------------------------------------|
C#|-7-7--7-7--7--8-8-8-10-8--7-7--7-7--5--8-8-8-10-8-|

Chorus: (1:35)
F#|-------------------------------------------------------------------------------|
C#|-------------------------------------------------------------------------------|
G#|----------8-8-8-7---5-5-5-5---------------------8-8-8-7------------------------|
C#|-7-7-7-7---------------------5-5-5-5---7-7-7-7------------8-8-8-8--10-10-10-10-|

(Chorus Cont., 1:44)
F#|-------------------------------------------------------------------------------|
C#|-------------------------------------------------------------------------------|
G#|----------8-8-8-7---5-5-5-5---------------------8-8-8-7------------------------|
C#|-7-7-7-7---------------------5-5-5-5---7-7-7-7------------8-8-8-8--10-10-10-10-|

Bridge: (Starts at 1:54, bass comes back in at 2:13)
F#|---------------------------------------------------------------------------------|
C#|-7-7--7-7~--8-8--8-8~-7-7--7-7~--8-8--8-8~-7-7--7-7~--8-8--8-8~-7-7--7-7~--5-5-5-|
G#|---------------------------------------------------------------------------------|
C#|---------------------------------------------------------------------------------|

Pre-Chorus: (2:32)
F#|---------------------------------------------------------------------------------------------------|
C#|---------------------------------------------------------------------------------------------------|
G#|---------------------------------------------------------------------------------------------------|
C#|-7-7--7-7--5--8-8-8-10-8--7-7--7-7--5--8-8-8-10-8--7-7--7-7--5--8-8-8-10-10--7-7--7-7--5--8-8-8----|

Chorus: (2:52)
F#|-------------------------------------------------------------------------------|
C#|-------------------------------------------------------------------------------|
G#|----------8-8-8-7---5-5-5-5---------------------8-8-8-7------------------------|
C#|-7-7-7-7---------------------5-5-5-5---7-7-7-7------------8-8-8-8--10-10-10-10-|

(Chorus Cont., 3:01)
F#|---------------------------------------------------------------------------------|
C#|---------------------------------------------------------------------------------|
G#|----------8-8-8-7---5-5-5-5---------------------8-8-8-7--------------------------|
C#|-7-7-7-7---------------------5-5-5-5---7-7-7-7------------8-8-8-8--10-10-10-10~--|

(No bass from 3:13 to end.)

And that's it! Easy song, fun to play.