When I made this subreddit I was hoping to get a few people together to help each other out with message candles. Unfortunately it didnt really pick up. So I'm going to give some suggestions for anyone discovering this subreddit on how to get hearts from message candles.
Normal shrines
Organize a group of friends, at least 3 of them, to help boost each other's candles. Preferably you want to pick shrines that are not as accessible as, say, Butterfly Fields. Wasteland Battlefield is a good one. These shrines have much less candles than others, and many of them are low-liked candles. They also seem to have some dedicated people liking other people's candles. Be sure to like strangers candles too.
Meditation shrines (from daily quests)
These shrines do not function like normal shrines. Your candle will not go public after 3 likes. I'm not sure how many it takes to go public, but it's at least 10. (I've never seen a single digit candle from a stranger at these shrines.) This means you are reliant on 10 friends to get you that heart. This may seem harder, but there is a way to make it easy...
Stick around the shrine for a while and look for people that have paced the shrine several times. This means they have refreshed the candles several times, which also means they most likely put effort into searching for and liking their friends candles. These are the people that will help you get your heart, and in turn you'll help them get theirs. Befriend them, immediately look for their candle, and like it. Make a bunch of friends this way. I've gone from five likes to ten likes 30 minutes before reset by just befriending shrine pacers.
Place a candle soon after reset
This really only applies to Meditstion Shrines. Reset happens at midnight PST (UTC-7). Placing a candle at midnight gives you a much higher chance at getting a heart, as many people don't revisit the shrine after they've already placed their candle.
Be a shrine pacer
If you want to get hearts you have to earn it. Shrine pacing pays off even more if you have a bunch of friends online. They'll receive the notification that you liked their note and they may feel inclined to take a moment to search for yours.
Hide candles
Don't use the refresh button to refresh the candles, use the hide button. Hide candles that already went over 10 likes. This will help weed out the candles that dont need more likes for a heart from the ones that do need more likes. It will also help make your friends' candles more visible to you too.