This can be so exhausting and heartbreaking to work through. I suggest figuring out WHY you are shooting for this, and use those reasons as reminders (as encouragement) when you are feeling like giving up. If it is merely because other people say you should - then maybe this isn't the right decision right now.
We struggled with my daughter a few times with this. Different things worked at different stages in her life. Found we ended up having to tackle the problem again after long visits to family in which her routine had been altered.
When she was little - putting her down when she was calm and not yet asleep.....staying and patting her back and 'shooshing' seemed to work. The key was to only provide this reassurance of touch and sound when she was fussing and to stop immediately when she stopped fussing. Initially this took HOURS, and each night it took less time, until we were no longer doing it. You must have some endurance for the first few nights to outlast and stay consistent.
When she got older - touch and sound were more likely to wake her up, so the previous technique no longer worked. Instead I followed advice from SUPER NANNY. This technique is for the child that will stop crying the moment you pick him/her up - indicating they are just wanting to be with you and that nothing else is really the problem (assuming you have already made sure they have a clean diaper and fully belly etc.) She suggests that you put the child down and walk out - they start to wail....count in your head until you return in to see them. Lay them back down and walk out again. No eye contact, no talking - not trying to engage them. They will wail again - this time wait 2x as long as last time. Keep doubling the time. It took 3 times of me going in to lay my daughter down before she settled in. Now if we need to do it, it usually is one time. IT WAS HARD.
I wish you luck - there is NO one right answer!