Alright, this is a bit crude but it will work for all intents and purpouses. If you have any further questions on this subject you can send me a note thru DA.

First And Foremost: IMPORTANT!!! READ!!!!
--This tutorial is for PHOTOSHOP. It may work with other paint programs, though.
--This tutorial is ONLY FOR THOSE WITH TABLETS!!! A lot, if not all, of this inking technique is relied heavily on pressure sensitivity that you can ONLY get with TABLETS!!! If you want to try it with a computer mouse, be my guest, but you will NOT get the same results.
--This tutorial is NOT for those with shakey hands. You have to have a pretty steady hand to ink like this properly.
--This tutorial is NOT for those without patience. Some of this can get tedious...so BEWARE!
--This tutorial assumes that you have a basic knowledge and understanding of PHOTOSHOP. It's pretty self explanitory, though, so all should be well.

Now, on with the show! :3

PREP WORK.
Before even thinking of getting your artwork into Photoshop, you want to scan it into your computer. When you are working with a sketch that is needing to be Digitaly Inked, you want the original sketch to be as large as possible. When you scan in the sketch you wish to ink, make sure you are scanning it at a resolution of 300dpi (dots per inch) or larger. Then it will be at a large enough resolution to give you a good depth to ink at. Also, just leave the image as a gray scale.

STEP 1.
Once you have your sketch scanned in open the saved file into your PHOTOSHOP program. You'll want to make sure that the image is set to RGB by going to Image--> Mode--> RGB Color. You should end up having a nice gray toned pencil sketch loaded up into Photoshop.

STEP 2.
At this point the sketch may be a bit to light and gray to be working with for digital inking. What you want to do is make the pencil sketch a lot darker and defined. To do this you will want to bump up the contrast and brightness levels of the image. Go to Image--> Adjustments--> Brightness/Contrast. Once the dialouge box comes up, you will have to play around with the sliders to get a nice rich appearence to your sketch. Nice darks and bright whites. Usually you get this by increasing both numbers on the slider. DO NOT WORRY ABOUT QUALITY!!! If the sketch gets kinda pixalated or to hard edged, thats fine, the sketch is only there as a base for the lineart, you'll be tracing over the original sketch and deleting it latter anyways.

STEP 3.
Now it's time to drop the opacity of the image. First, you'll want to copy this sketch to it's OWN NEW layer. To do this you will want to take the layer the sketch is on and drag it to the "make new layer" button so it is ABOVE the background layer (or just right click on the layer and click on "Duplicate Layer"). Now you will have TWO copies of the same image. Click on the bottom layer of the two and go to Edit--> Fill so that the bottom layer is COMPLETELY white.
Click back on the top layer that still has the sketch and drag it's OPACITY *circled in red* down just enough that the sketch is visible but barely. I usually keep the image down to about a 30% - 40% opacity, but whatever works for you.

STEP 4.
Once you have set the opacity, click on the "make new layer" button, or go to Layer--> New--> Layer. Make sure that this new BLANK layer is ABOVE the pencil sketch. You may want to name it as 'Line Art' as I have above, underlined in red. Once this is done, you want to make sure that you are at FULL VIEW of your image. Then pick a solid hard round brush to work with. I usually work with a 3 to 5 pixel brush as shown. You will want to drop the opacity of the brush just slightly, somewhere between 60% to 90% and the fill of the brush to around 80% or above. This will give the line a little bit more weight. But the settings are really up to you on what you like.
When inking, use light strokes, and go over areas MORE THEN ONCE. It helps give a light of varience in the line. DO NOT WORRY if the line's are PERFECT. Trust me, it's at FULL VIEW, once you zoom out the ink work will look a LOT SMOOTHER :3 That's why it's IMPORTANT TO INK BIG!!!!

STEP 5.
Now, this is just me, but it's a good tip. You will probably want to make seperate layers for different areas you are inking. This is because you WILL HAVE to go back in some areas to erase, and you don't DON'T want to erase over areas that don't need to be. So in this step I have inked the hair on a different layer then the body, this layer being called 'Line Art 2', underlined in red. What isn't shown is that latter on the cloths and some detail work like gems all have their own layers. Once you have inked the entire image with multiple layers, you can go back and merge the entire image before coloring. So it's worth it to INK ON MANY LAYERS. Usually, depending on the size and detail of an image, you can get between 4 to 10 layers of ink.

STEP 6.
If you have inked an area and it came out REALLY REALLY rough, there is a pretty easy way to fix it, yet it gets rather tedious. You'll want to zoom in about once, or twice, into the image area where you want to 'smooth' things out as shown. Make sure you are on the layer you want to work with.

STEP 7.
Once zoomed in, pick a decent sized eraser brush at full just under full opacity. Around 90% or so. Here I'm using a 9 pixel hard round brush. Just go in and erase the areas that don't look right and or are messy. If you erase into the linework you want to keep, it's ok, you can go back in at the same zoom level and touch up and smooth out where you erased. This can be a pain sometimes, but the results are WELL worth it ^_^.

STEP 8.
Now, just go thru all these steps untill the image is fully inked. Once it's done to YOUR satisfaction, you can hide and or delete the original pencil sketch, and you should be left with a nice, clean, crisp line art that is all ready and prepped to be colored :3 In the image above you can see what the sketch looked like before the ink job and after the ink job. Nice eh?

OPTIONAL STEP 9.
This step you DON'T have to do, but I think it gives the digital ink a little more 'kick' if you will ^_^. Once the inking is done make sure ALL YOUR INK LAYERS ARE MERGED TOGETHER! Take the ink layer and duplicate it as you did in STEP 3. Now, click on the bottom ink layer of the two and go to Filter--> Blur--> Gausian Blur. When the dialouge box comes up you'll want to set the blur effect to a fairly low number. I usually keep the blur at 2.0 *circled in red*. But you can make the number whatever you like to get the desired effect.

OPTIONAL STEP 10.
This bluring of the bottom ink layer gives the inked line art a softer feel. It's not VERY noticble, depending on how much you blur, but I think it's enough to give it a nice soft feel. ^___^ but that's just something I like to do, it's optional. You can see the difference in the image above, it's subtle, but it works. And since it's on a seperate layer, you can always just delete it if you don't like it and NOT ruin the original ink layer.

Welp, that's about all folks!!!!! Not anything fancy, just how I like to do things. Hope it gives some of you a better idea on how to get nice smooth inks digitally ^.^d