It's a pretty safe bet that your first recordings will have some problems, so let's go over some very common ones and show you easy ways to fix them.
Recap of Signal Chains
Keep your signal chains simple. Don't use excessive wiring if it's not necessary—the simpler the chain, the better. This is especially important when dealing with gain stages; you have to be very careful about levels. Any device that can raise and lower your gain (any device with a volume control), such as a mixer, preamplifier, or input trim control, must be used carefully. It's easy to make mistakes like using two gain stages when only one will do, possibly adding noise or easily clipping the signal. Remember, once you clip a signal by overboosting it, your take is destroyed. You can't mix out clipping in a track. So be careful!
Ground Loops and Buzz
So you have some noise. Where is it coming from? There are a few very common buzzes, and most are easily remedied. Most buzz comes from bad grounding, which can create what is known as a ground loop. Modern houses typically utilize three-prong electrical outlets; the third plug is a ground, which draws excess electrical charges away from a power source. If an electrical outlet is not grounded properly, every device plugged into it might buzz. This can include your amplifiers or even your recording devices. Buzz is annoying and can ruin a recording. Fortunately, there are a few things you can do.
First, try the easiest fix: Plug the source into a different power outlet. Amazingly, some outlets buzz less than others. If that doesn't work, purchase a power conditioner, a device that regulates the type of power that comes out of an outlet, making sure the power is regular and clean. If that doesn't work and you have a really bad buzz problem, call an electrician to look at the wiring in your house. This can be costly, but it might be a viable option if the noise is rendering your expensive gear useless. Direct boxes are also susceptible to ground loop buzz. Thankfully, most direct boxes come with a ground lift switch that eliminates the buzz when activated. If you're planning to purchase a direct box, look for one that contains a ground lift.
Noises of All Kinds
Ground loop is not the only kind of noise. Electrical equipment, especially delicate equipment such as microphones and recording devices, is prone to interference. Interference from radio signals, televisions, and magnetic sources can create problems. It's not uncommon for a public address system to occasionally pick up a radio station or a cordless phone signal, and you might run into these problems in your home studio as well. The most common problem that home studio users face is from magnetic interference. If you've ever put a magnet near a TV, you've seen the color go haywire. Studio monitor speakers contain large magnets as part of the speaker. If you run a computer-based studio with a tube monitor, the speakers could interfere with the signal in the computer (not to mention that magnets should be kept away from hard drives). Look for monitors that are magnetically shielded. Many monitors are designed this way due to the popularity of computer recording, but you should double check to be safe.