A.H.
With both of my kids, I let them cry it out a little at a time around the age of 4 months. I would do the bedtime routine, rock them until they were somewhat sleepy, but not passed out yet, then lay them down in the crib. Then I would leave, and if they were crying, I let them cry for about 5 minutes, went back in and rubbed their belly (sometimes I would pick them up and rock again) until they settled down, then leave again. Then I'd wait 10 minutes and if they were still crying, I'd go back in and rub their belly (when they were older, they'd roll onto their bellies and then I'd rub their back) until they settled down again. Then I'd leave and if they were still fussing, I'd wait 20 minutes. I wouldn't go in unless they were really screaming. If they were just whining or babbling, I'd leave them. After doing this for a few days, I almost never had to go in a third time. After a couple weeks, I almost never had to go in a second time even.
My son is 7 months and my daughter is almost 2. Now, we only have problems when they are ill, are trying to reach a milestone (like standing up or crawling), or have nightmares. With the younger one, we go back to the 5 min/10 min/20 min cry it out plan, and we only have to do it one or two nights. With my older one, we just tell her to go back to bed and she does.
Whatever you decide to do, be consistent.