Install a quality interface for importing audio into your computer. While contemporary sound cards are capable of excellent performance, connecting equipment through mini-plugs represents a compromise. Interfaces are available in many forms, from USB and Firewire to PCI cards with or without breakout boxes. Consider a minimum standard for high quality to be 24-bit, 96 kHz sampling.
Use at least one good microphone preamplifier and a large diaphragm condenser mic. The preamp in your interface may qualify as "good," but much depends on the combination of preamp and mic. For that matter, choice of mic can depend on the type of music you record or even the sound of the voice of your lead singer. Try different combinations of preamps and microphones until you have sounds you like.
Choose a digital audio workstation (DAW) software that suits your work method. Pro Tools is regarded as something of an industry standard; however, the term "pro tools" is becoming increasingly generic, so that any time a computer is used for audio, someone will refer to the process that way, regardless of the software in use. Excellent DAW programs for the PC include SONAR, Nuendo and Cubase, as well as the ubiquitous Pro Tools. You may already have DAW software included with the interface or preamp you use.
Selecting monitors is another critical step in assembling a studio capable of superior quality. Home stereo speakers are designed to flatter music, and indeed all speakers will color the sound of what they produce in some way. Speakers designed for monitoring will attempt to minimize this effect. Headphones can be used for critical listening, but without years of experience, not to mention top-quality headphones, you should avoid these for mixing. Headphones will be needed for monitoring when using microphones.
Consider the acoustics of the space in which you will work. Home-based studios are often in rectangular spaces with parallel walls. Techniques such as nearfield monitoring and close-miking can reduce the impact of less than ideal room sound.
Add to your knowledge continually. Tools are only as good as the craftsman using them, so the learning process should never end. Recording music is such a vast and varied pursuit that your personal interests will influence what you need to know, and how you will use your computer recording capabilities.