This guide will show you step-by-step how to start mining. It assumes you have a desktop computer with a graphics card and you are running Windows.
Mining bitcoins is not likely to be profitableDespite what you might think or read, the truth is that it is difficult to make a profit from mining bitcoins if you are starting out now. This comes from the fact that so much bitcoin mining equipment has been manufactured and sold that the difficulty will continue to increase at an incredible rate for at least another six months. This rising difficulty has reduced the likely return on any further investment to below zero. You will not make a profit unless you can buy hash rate (including all equipment, cloud hashing, and mining contracts) for less than 0.02 BTC per GH/s and you start mining now (January 2014).
Please keep in mind that when I mention profit, I mean profit in terms of bitcoins, and not your local currency. If you cannot make a profit in bitcoins, then it is better to buy the bitcoins directly rather than to buy the equipment to mine the bitcoins. This is true regardless of what happens to the value of a bitcoin.
Mining alt-coins can be profitableCurrently, it is profitable to mine alt-coins if you have a desktop computer with a graphics card. However, ...
You should not mine using a laptop. The stress on the laptop is high, and replacing the laptop will cost more than you will earn from mining. If you have an Nvidia graphics card or a GPU on the motherboard, then your revenue will be very low and will not be enough to even pay for the electricity. Regardless, it wouldn't hurt to give mining a try even if you have laptop or an incompatible GPU, as a learning experience.
Assuming your computer is already paid for, the costs of mining with a graphics card on a desktop computer come mostly from power costs, though there is some cost due to wear and tear. If you get free electricity, then making a profit from mining is easy. In fact, you can probably make a profit mining bitcoins, but mining alt-coins is currently more profitable.
Step 1. Determine the hash rate and power usage of your graphics cardFind out what kind of graphics card you have. It helps to have as much information as possible about it. Then, find it these lists:
https://litecoin.info/Mining_hardware_comparison and
https://en.bitcoin.it/wiki/Mining_hardware_comparison#AMD_.28ATI.29You want to find the hash rate (kH/s for litecoin, MH/s for bitcoin) and power usages (watts). Unfortunately, these lists are mostly incomplete. Do your best. The bitcoin list states hash rate in MH/s but don't worry about that yet. Also, the exact numbers are not required because they are only used here to estimate your profitability.
Step 2. Determine your cost of electricityLook at your power bill. It will tell you how much yoru electricity costs. If you electricity is free, then your cost is 0.
Step 3. Enter you hash rate, power usage, and power cost in the profitability calculatorGo to
dustcoin.com. Enter your hash rate. Enter the same number for both SHA-256 and scrypt. Make sure that MH/s is selected for SHA-256 and kH/s is selected for scrypt (scrypt is about 1000 times slower than SHA-256). Add 100 watts to your graphics card's power usage and enter that value under Power. Enter your power cost. Select Day for the Period.
Step 4. Determine if you can make a profit from miningThe table will show you approximately how much you will make mining each kind of coin for an entire day. It is likely that mining SHA-256 coins (such as Bitcoin) will show a loss, but mining scrypt coins should show a profit between $0.50 and $4.00, depending on the values you entered. Going forward, I am going to assume that you will be mining scrypt coins.
Step 5. Install mining softwareDownload cgminer version 3.7.2 from here:
http://ck.kolivas.org/apps/cgminer/3.7/. Later versions don't support graphics cards, so get the 3.7.2 version. Unzip the file to a convenient location, such as C:\mining.
Step 6. Set up an account at multipool.usGo to multipool.us and create an account by clicking on Register.
Step 7. Create a shortcut for convenienceOpen Windows Explorer and navigate the folder where cgminer is installed. Right-click on cgminer.exe and select Create Shortcut. Right-click on the shortcut, click on Properties, and add the following to the Target text:
--scrypt -o stratum+tcp://pool1.us.multipool.us:7777 -u .1 -p x
where
is your multipool user name. The password can be anything.
My Target looks like this:
D:\mining\cgminer-3.7.2-windows\cgminer.exe --scrypt -o stratum+tcp://pool1.us.multipool.us:7777 -u odolvlobo.1 -p x
You can move this shortcut to your desktop.
Step 8. Start mining
Double-click on the shortcut. A window like this will appear:
Lines saying "Accepted" should start appearing. If they all say "Rejected" then something is wrong.
Note the hash rate at the top. After a few seconds, it should be somewhere around your expected hash rate. If not, there are several things that might be wrong. I'm not going to troubleshoot the possible problems here, but the most likely fix is to add a -I parameter with a value between 8 and 20. You will have to experiment to get a good balance between hash rate and usability. I use "-I 13" or "-I 19".
You can check your results and profits at the multipool.us website.
Type the Q key to stop mining.
Next steps.
1. Optimize your mining setup. cgminer has many configuration options. Some might improve your hash rate. Do some research.
2. Set up an account on Cryptsy or Bter. You will be mining many different types of coins. If you don't want to keep them all, you can transfer your coins to Cryptsy or Bter and sell the ones you don't want and buy the ones you do.
3. Try other mining software and other pools.
4. Learn about how mining works.
5. Learn how the difficulty and the exchange rate can affect your profitability.
6. Learn how to predict future mining revenue so that you can invest profitably. 
