Whats the best way to capture familiars?

It's pure luck whether or not they will get the hearts above their head and let you catch them. Just make sure when that does happen that you switch to Esther and play the song to tame them before they run away.

At that point in the game is it purely up to luck. Sneaking up on enemies does not make them easier to catch. All you can do is knock them out and hope for the best. The banana monster has a 6% likelihood of being tamed which is rather low.. so it can take time.

*Potential spoilers*

Later on in the game you can purchase a power using errand stamps that improves the likelihood of taming familiars.

The % don't really matter because you can capture some low % on first try while some 20% in 50 tries so it's mainly just fight that certain enemy over and over til you get it.

4% - 10% is the different capture rate between good vs normal familiar.
When you release all of your familiar(some can not be release), you will notice that capture rate increase to 25% or more.

Each creature type has a certain % chance to be captured. I actually had the same issue at this point in the game. Later on there is a stamp reward that increases you chance to capture or tame familiars. if you want to wait. If the creature types are on the map definately go for those so you know they will for sure be in your battle. You can enter and leave al mamoon if your not seeing that creature type on the map to avoid random battles those creatures are not in.