First off, this technique works best (but not exclusivly) with a bass, as guitar strings are generally too small and easy to push down to simply to this technique.
I suggest you tune your bass standard (EADG), as any drop tunings lower the tension on the strings, making them easier to push down and lowering your results (very, VERY little, but lowering them nevertheless).
Anyway, onto the lesson. You can start by playing this pattern up the neck:
G|-------------------------1-2-3-4--5-4-3-2------------------------------|
D|-----------------1-2-3-4--------------------5-4-3-2--------------------|
A|---------1-2-3-4------------------------------------5-4-3-2------------|
E|-1-2-3-4----------------------------------------------------5-4-3-2----|
Play the first four frets, decending a string every time. Once you finish on the last string, slide up one fret, then do the pattern backwards. Once you get back to the first string again, slide up yet another fret and start the exercise over again. A good place to stop is on the 9th fret (pinky should be on 12th), but you could easily continue your way up the neck.
Play this a few times. Does it burn yet? Gooooood... That means its working!
You should probably notice that you're playing it faster each time without realizing it. It should also get easier and easier with each repitition.
Another exercise is this:
G|-0h1-0h1-0h1-0h1-0h1-----------------------------------------------|
D|---------------------0h1-0h1-0h1-0h1-0h1---------------------------|
A|-----------------------------------------0h1-0h1-0h1-0h1-0h1-------|
E|-------------------------------------------------------------------|
I'm running out of room with that tab and I'm too lazy to add another, but you get the picture anyway. Just hammer on from the open string to the first fret repeatedly, starting with the G string. You could continue this pattern with your other fingers like this:
G|-1h2-1h2-1h2-1h2----------------------------------------------|
D|-----------------1h2-1h2-1h2-1h2------------------------------|
A|---------------------------------1h2-1h2-1h2-1h2--------------|
E|--------------------------------------------------------------|
...And so on, followed by:
G|-2h3-2h3-2h3-2h3----------------------------------------------|
D|-----------------2h3-2h3-2h3-2h3------------------------------|
A|---------------------------------2h3-2h3-2h3-2h3--------------|
E|--------------------------------------------------------------|
Continue this pattern until you get to the point where you hammer on from the 4th fret to the 5th fret. Of course, the number on hammers on you do before you go on to the next string is entirely up to you. It could be 5, it could be 50. Personally, I did it 50 times because I'm an overacheiver.
To give yourself even more of a challenge, do all the frets on a string before moving to the next, keeping your other fingers down as you move to the next finger. Because I'm so horrible at describing this with words, here's a tab diagram:
Hold 1st fret: AND 2nd fret: AND 3rd fret: ...
G|-0h1-0h1-0h1-0h1-1h2-1h2-1h2-1h2-2h3-2h3-2h3-2h3-3h4-3h4-3h4--|
D|--------------------------------------------------------------|
A|--------------------------------------------------------------|
E|--------------------------------------------------------------|
Continue that up to the next string, then move up to the next string. If you do this enough, your hand/wrist WILL hurt.
I recommend you play the first exercise more extensively, as it not only increases finger strength and precision, but also increases speed. The 2nd excersize is mostly focusing on finger strength, and some bonus hammer on practice!
To finish up a little info on me: My name's Brian, I'm 15, been playing bass for about 3 years now, guitar for almost 2, and drums for about 10 months. I'm also a singer.
I'm DEFINETLY not expecting this lesson to be the greatest ever, since its my first, and its 4 o' clock in the morning as I type it... But the point was to share this (I think) easy and effective strength/precision exercise.
Thanks for reading, putting up with my God-awful tabs, and I hope I helped!
/ my profile 
