Footprinting is not a particularly huge subject, but it is not lacking in size. Before we begin our endevours to Footprint you probably will want to visit here (http://darkpontifex.dajoob.com/Footprinting.zip) Its my website an has a variety of footprinting tools which will interest you.

Footprinting to be frank is finding out about your victim. We are assuming the previous attacks have failed. What do you know about your victim? local sports teams, family member names, all sorts of stuff like that. Do you know if they are having technical difficulties? Once again it's what you know about your victim. Personal information is extremely important, and you should probably scribe it to a .txt file for worlists etc. However we primarily will focus on the technical aspect of footprinting.

DNS Zone Transfers/Subnets/General Info->

There is a site inside my file, Sam Spade which has all sorts of DNS info on site, you could unviel site aliases, and or parent corporations etc. (NEW TERMINOLOGY - DNS, servers which turn IP addresses such as 123.123.123.123 into alpha characters which we can read such as "yahoo.com" of course if you want to you could go directly to the IP but that is hard to remember and such DNS servers were invented.

WHOIS->

This tool identifies all of the IP addresses on the internet and where they reside. This can be very useful for indenifing all sorts of things.

Google->

Ahhh The Power of google. The sitedigger tool automatically searchs for vulns in a site identified by google, how useful!

Ping Sweeps->

Do you roughly know your target's IP range? If so you should do this with the ping pack tool to determine active computers on the network. (NEW TERMINOLOGY - Ping, a small (or large) bit of data which is sent to an IP and then sent back to determine network connectivity)

Other Stuff->

As I said Personal or local info is beyond value for a hack. Visual route can easily show you information coming from an IP and where the IP is, future versions support tracing beyond proxies. Webferret is a general good tool in case you need some goodies about a site or an IP.

That is a summary of Footprinting, as I said it is not very big, but none-the-less very important. Of course there are many other tools you may prefer to use, these are just the most common and my personal favorites.