It literally only took me an hour to tame a level 145 with only 50 mejoberries.
1. Gather berries and put the berries in your last slot
2. Kneel down and walk up to one of them and feed it the berries
3. Now you just follow it around while kneeling down and feeding it berries whenever it's hungry
4. Congratulations you tamed one.
Since they're commonly found in the red wood forest, I recommend only taming one if you're close to water as if you get attacked by something you can jump into the water to get away. Then when you think it's safe just go find your monkey and go back to following/feeding it.
Easy to tame, just sneak and bring one soothing balm and berries but i prefer mejoberries. If your looking for one of these go to the redwood forests and you might find one just search for it, but becareful the terror birds might attack you or purlovias the sneaky rat. (Up if this is helpful)