If you are new to pen and ink as a medium, I should warn you that it is possibly the most tedious of mediums, and one that is unforgiving. If you make a mistake its permanent. The best you can do is turn it into something! Despite this a detailed pen and ink drawing can hide a lot of indiscrepancies that would be more obvious in other media. Here is how I went about creating a typical drawing.
First select your subject. What works well is an image that has lots of detail across it. I find multi-level town and cityscapes work well, as does anything with an elevated viewpoint. In this case I've selected a view of Sherborne taken from a slope just outside the town. With all paintings I start by sketching out in pencil the rough positions of the shapes that make the image. With fiddly pictures like this its absolutely essential. I usually start with the main feature, setting its proportions so that the resultant image will be about the right size for the piece of paper I'm using (a relatively smooth cartridge paper is fine). I then work out left and right up and down from that feature, and typically find that features get squashed or stretched when I get further out. This happens as small innacuracies build up across the paper. To fix, refer back to the image you are working from and rub out as necessary where the innacruacy started. One very important thing - AVOID TOUCHING THE PAPER - hand contact with the paper leaves oily residue that prevents the ink adhering. I recommend using a tissue to rest your drawing hand on. One other tip - its worth acquiring the draughtmans skill of rotating the pencil as you draw - this keeps a well defined and reduces the need for sharpening.
Once everything is proportioned in pencil its safe to put pen to paper. Here you have the choice of a fine tipped drawing pen, or my tool of preference - an old fashioned dipping pen. I would advise against using biros as the ink tends to build on the point and come off where you don't want it. It takes a skilled hand to avoid that. If you do decide to use a dipping pen don't be tempted to flood the nib with ink so it goes further between dips, as you have less control of ink deposition that way. The ink bottle I've used here has a dropper, which is just perfect dropping a single drop on the nib.
Having drawn out the picture in pencil, you can start anywhere with the pen. A picture like this with lots of overlapping features may be best attempted from bottom to top - this avoids the problem of finding you need a foreground chimney where you've already got a dark background. In this case though I've started with the main feature and tried to take note of anything that overlaps in front. When drawing make sure to AVOID TOUCHING THE PAPER still - use a tissue to lean on.
When it comes to shading the usual technique is cross hatching - parallel lines filling the space in one or more directions. Try to use a direction of line that suggests the surface it represents - so for roofs try horizontal plus diagonal at the same pitch as the roof. For dark areas use 3-4 directions of line, for light areas no more that 1. You can make lines lighter by using the pen lightly and quickly. If its a nibbed pen try turning it slighty for even lighter lines so the nib isn't flat against the paper. I've found that I can do cross hatching reasonably by turning my wrist for areas less than about 2cm acorss. For larger areas I either break it down, or keep my wrist stiff and bend my elbow - this keeps the lines straight. The main problem though is getting lines precisely to the edge of the shaded area - a slower stroke helps, as does careful addition of any missing bits of line afterwards - I said this was tedious!
For natural vegetation I do not cross hatch, but instead 'squiggle'!
To finish off you might like to add selective colour to help pick out the features. Before you do this though, rub out any pencil lines still showing. Any water based colour is likely to make the ink run, and coloured ink doesn't tend to give a good result, so I generally use coloured pencils to lightly shade areas. Its easy to get carried away and the result can be a bit of a muddle, but because you are using pencil over permanent ink, you can try different combinations, running out what you don't like before settling for the final combination. Here I've chosen to highlight the abbey and associated buildings and the natural vegetation, and then knocked it back a bit to make it more subtle.