Whether you’re breastfeeding, formula-feeding or doing a combination of both, chances are you’ll eventually use a bottle with your infant. While images of a parent blissfully holding a bottle make the process look easy, but you need to know about how to bottle-feed a baby safely and happily.

When it comes to figuring out how to bottle-feed a baby, selecting an appropriate bottle and nipple is step one.

There has a tip for all parents: Look for a bottle that’s easy to take apart and clean. That generally means a nice wide neck and the fewest parts possible. Proper cleaning is so important, so choose the simplest bottle, which may just have a nipple, bottle and collar. If your child seems happy and easily takes the bottle, then there’s no need to switch.

Of course, it’s also important to pay attention to the flow of the nipple, which varies based on infant age. Generally speaking, young babies need a slower flow, while older babies who’ve mastered the art of bottle-feeding can handle a faster flow. The nipple may be called “slow flow,” “medium flow” or “fast flow” or may be numbered from one to three, with one being the slowest flow. There is no standard of flow between different brands, but most newborns should begin on level one or slow flow.

So how can you tell when it’s time to change the nipple size? Some infants happily use the same flow nipple throughout their infancy, while others may need a faster flow nipple. “If you notice your child taking a long time to finish a bottle, or losing interest midway through feedings, a faster flow nipple may be needed, this might happen at around 3 or 4 months of age, with another potential upgrade around 6 or 7 months.

If your infant finishes a bottle quickly (say, under five minutes), seems gassy or cranky, or spits up a lot of milk right after feedings, it may be time to go back to a slower-flow nipple.