General Rules for Pricing Magic Items

Continual Items: These items become functional when they are worn, held, or attuned, but after that, they are always active. Some items even passively have effects on all who are near. Rings and rods are often continual items, but they don't have to be.
Actived Items: These items require the player to take an action to turn them on, after which they function for a duration before turning off again. These items are often command word or attuned.
Consumable items: These items are gone after they are used. Potions and scrolls are the most common comsumable items, though some wondrous items also function this way. Consumable items almost always function exactly like a particular spell.
Charged Items: These are consumable items with a lot of uses (usually 10-50). The price per charge is cheaper than buying a bunch of consumable items. The item itself can be re-charged as long as it has at least 1 charge. After that, it goes inert and is no longer magical.
Staves: Staves hold magical essence and make it so their weilders don't need to prepare certain spells. Staves have rules of their own for calculating costs.

Depending on the function determined above, calculate the Base Cost of the item.
Items may have more than than one type of function. If so, price them separately and add them together. Usually all effects on an item are considered primary effects. However, if two spell effects are very similar, the cheaper ones can be considered Secondary effects (75% costs)
Be sure to always add the cost of spell components and the masterwork cost of the item itself to the base cost.
After all the item's costs are totalled, apply adjustments.
Remember that these tables are only an estimate, and with all magic items, there are edge cases that will break the rules. The GM always has final say on the cost of a magic item.
Other Considerations when making magic items.