Step 0 - Install Homebrew
Here is an article on how to install Homebrew Package Manager.

Step 1 - Install SDKs

iOS & macOS
Visit the Apple Developer

brew install --cask android-studio

brew install --cask android-SDK

brew install --cask android-ndk

brew install --cask flutter

Step 2 - Update Your Path

Mac OS X default can be this.

vi ~/.bash_profile

## ## ## ## ## ## ## ## ##
## Flutter
## ## ## ## ## ## ## ## ##
export PATH="`pwd`/flutter/bin:$PATH"

Step 3 - Run Flutter Doctor

flutter doctor

/usr/local/Caskroom/android-sdk

Install Xcode

sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer/

Accept License

sudo xcodebuild -license

Open an iOS Simulator.

open -a Simulator

Step 4 - Create a Flutter Project

flutter create my_first_app

Step 5: Deploy to iOS Device.

brew install GCC

brew update
brew install --HEAD libimobiledevice
brew install ideviceinstaller ios-deploy cocoapods
pod setup

Step 6 - Android
If you need help, this Stack Overflow is helpful.

flutter config --android-SDK

Step 8 - Start Application

flutter run