Our new Indie Games subforum is now open for business in G&T. Go and check it out, you might land a code for a free game. If you're developing an indie game and want to post about it, follow these directions. If you don't, he'll break your legs! Hahaha! Seriously though.
Our rules have been updated and given their own forum. Go and look at them! They are nice, and there may be new ones that you didn't know about! Hooray for rules! Hooray for The System! Hooray for Conforming!
Generally speaking, it's just like any other skill: practicing helps, and practicing well helps prevent bad habits from developing. I have some general feedback I can offer, but I'd like to preface that I'm by no means a professional nor a wealth of experience teaching voice.
Screeching can mean some of a few things are happening:
* You just don't have enough breath to get you through the run. The majority of bad sounds you'll make come from a lack of air to serve as a foundation for your note. Look up how to breathe with your diaphragm. This is an important but hard to learn technique because, at least for me, it's based on feel.
* Something that helped me a lot, especially with multiple pitch changes, is to slow down and internalize the order and sound of each pitch. Identify each note in a run that you're having trouble with, hum each note, do the whole run slowly at a hum, then sing a vowel through it, then add the words and speed it up.
* A mental exercise that's worked well for me is that while I'm singing, I focus on the upcoming notes I have a beat or two ahead of where I am, and not so much on the current one. Might be worth a try.
* It's possible you're straining your voice or outside of your range, but if you feel comfortable in the range you're in, that's not likely the case.
It's kind of hard to know in this instance what to focus on without hearing what's going on. If you want to send me a PM (or post here) a recording of yourself and what song you're working on, I can try to offer some more directed insight.