At this age (and up till they can roll over) they need the three S’s; they need to be Swaddled to sleep successfully. They need to Suck (breast, bottle or pacifier) and they need Sound (white noise or music but it needs to be the same every single time). Consistency is key.  
Every time they go for sleep it needs to be the same routine as much as possible and around 6ish months they start to get it. I liked to let mine fuss but not cry. Fussing is normal, they aren’t suppose to like to be away from you.  
You need to stay out of eye site as this comes into play later on because they will see you and cry for you. If they wake up all the way but aren’t fussing leave them alone. If they start to cry console by placing your hand on their chest but try not to pick them up, if you want to or the consuming isn’t calming in the first 30ish seconds pick them up and start the routine over again. If you can’t get them to sleep in 30 minuets stop trying.  
I’m assuming the age here but some days will be good and some days you’ll be a human mattress and that’s ok too! Some times you’ll get it once and sometimes it will take a swing to get them to sleep and sometimes you’ll nail it all day long. I’m on my third and it’s still hard for me too 😛.