Hey, when i first started bass lessons my fngers were so weak!
This exorcies will help you use finger per fret, strengthen them, and is 
good for a warm up.

Remember to use finger per fret, so you use your little finger just as much, 
it's shown on first TAB. Index — I
              Middle — M
              Third — T
              Little — L
Basicaly, use Index for 1st fret, Middle finger for 2nd fret and so forth... 
remembe to do this even when playing tab backwards, and not to use index for 
4th fret!

Here, just start off repeating this over.
|—I M T L—I M T L——I M T L———I M T L——|

G————————————————————————————1—2—3—4——|
D———————————————————1—2—3—4———————————|
A——————————1—2—3—4————————————————————|
E—1—2—3—4—————————————————————————————|

and play this backwards a few times too.

G—4—3—2—1—————————————————————————————|
D—————————4—3—2—1—————————————————————|
A—————————————————4—3—2—1—————————————|
E——————————————————————————4—3—2—1————|


Then after you get used to this as a warm up, try this.

G——————————————1—2—3—4—————————|
D————————————2—————————3———————|
A —————————3—————————————2—————|
E—1—2—3—4————————————————————1—|

and play this backwards.

G—4—3—2—1—————————————————4————|
D—————————2—————————————3——————|
A———————————3—————————2————————|
E—————————————4—3—2—1——————————|

All od these exorcises are very good warm ups for playing a song, or when practincing, 
but remember to use finger per fret as it aslo strengthens your fingers. 
You will find it hard to use your little finger at first, but just keep practicing 
and you can always move the TAB down to 5—6—7—8 to make it easier ro start with.

I hop ethis helped!
Ben Law ;)