Watch the Bends & Vibrato Exercise 4 online guitar lesson by Jeff McErlain from Beginner Blues-Rock Soloing
Pre-bends are particularly tricky, as it's very easy to start off out of tune. Often called "ghost bends", this is where we start off by already pushing the note up to our next pitch. As you can imagine, this can be a recipe for disaster, so it's important to put in the time when we practice.
It helps to make mental notes on how hard you work pushing the string. I often just go back and forth between a pre-bend and the fretted note just to make sure I refresh my muscle memory. Because that's what you're working on - muscle memory.