Summarize this article:

A soft reset essentially forces the phone to end all of its current processes, turn off, and then restart from a fresh state. No long-term data is lost you'll still have all of your apps, messages, and contacts saved to your phone after you perform a soft reset. The only data you risk losing is unsaved data in programs that are running when the phone turned off. Because a soft reset is quick, easy, and relatively risk-free, it's a good first step when trying to solve minor issues. Situations that might call for a soft reset include: You can't seem to receive calls or texts properly Your phone seems slow or "laggy" You can't seem to connect to wifi networks that you know are broadcasting correctly Your touch screen seems unresponsive or erratic An app has become frozen or unresponsive To start the soft reset process, close any applications that are currently open. Be sure to save anything that you're working on, like important texts or emails (note however, that most modern phones will automatically save drafts of your messages.) If the reason for the soft reset is that one of your applications is frozen and won't close, you don't have to waste time trying to close it. Just proceed to the next step. When you're ready to start your soft reset, slide off the rear casing. Carefully lift the battery out of its slot. This will cause the phone to immediately turn off. Give the phone a brief chance to "cool down" after removing the battery by waiting at least a few seconds. Then, simply replace the battery and turn the phone back on as you normally would by holding the power button down for a few seconds. This brief waiting period is something that's also frequently recommended when resetting everything from desktop computers to network routers. The reason for this has to do with capacitors small structures inside most modern electronic devices that store electric charge. Ten seconds is about how long it takes for most capacitors to discharge. Thus, waiting ten seconds before restarting your phone allows you to be sure that it's 100% "dead" before turning it back on. Another (slightly longer) way to soft reset your phone is simply to turn it off like you normally would by holding down the power button. Select "Power off" or "Restart" from the menu that pops up. Note, however, that if your phone is frozen, you may not be able to get a response this way, so removing the battery will be necessary. Note that some sources of tech knowledge (including executives from companies like Apple) recommend powering off a phone at least once every few days to preserve battery life. Since performing a soft reset by turning your phone off is so quick and easy, you may want to make it part of your regular schedule, especially if there are times of the day when you don't use it (like at night.) Another reason this can be a good idea is because it gives the phone a chance to (literally) cool off. The heat that can result from continuous use can eventually cause the lithium ion batteries in most phones to degrade.

Summary:
Use a soft reset for minor problems and service hiccups. Close all applications. Remove the phone's battery. Wait at least ten seconds before turning the phone back on. Alternatively, just use the power button. Consider powering off your phone semi-regularly.