Before you hack into a system, you must decide what your goals are. Are you hacking to put the system down, gaining sensitive data, breaking into the system and taking the 'root' access, screwing up the system by formatting everything in it, discovering vulnerabilities & see how you can exploit them, etc ... ? The point is that you have to decide what the goal is first.
The most common goals are:
1. Breaking into the system & taking the admin privileges.
2. Gaining sensitive data, such as credit cards, identification theft, etc. - not recommended
You should have all of your tools ready before you start the next steps too hacking. There is a Linux version called Backtrack. It is an operating system that comes with various security tools that will help you break into systems.
You must decide how you are going to achieve your task. Plan. There is a common methodology followed by hackers, I will mention it below. However, you can create your own methodology if you know what you are doing.
Common steps to be taken for hacking a system:
1. Reconnaissance (footprinting)
2. Scanning
3. Ports & Services Enumeration
4. Vulnerability Assessment
5. Vulnerability Exploitation
6. Penetration and Access
7. Privilege Escalation & owning the box
8. Erase tracks
9. Maintaining access
The above methodology can change based on your goals.
Before you break into a system, you have to collect as much info as you can on the system and target. You have to study your target well before