Example Gulp config for working with WP themes;

Gulpfile.js

/* 
	Package.json

	{
  "name": "gulpdev",
  "version": "0.0.1",
  "description": "",
  "main": "index.php",
  "scripts": {
    "dev": "gulp"
  },
  "author": "",
  "devDependencies": {
    "autoprefixer": "^7.1.4",
    "browser-sync": "^2.17.6",
    "gulp": "^3.9.1",
    "gulp-image": "^3.0.0",
    "gulp-jshint": "^2.0.2",
    "gulp-newer": "^1.3.0",
    "gulp-postcss": "^7.0.0",
    "gulp-print": "^2.0.1",
    "gulp-ruby-sass": "^2.1.1",
    "gulp-sass": "^3.1.0",
    "gulp-scss": "^1.4.0",
    "gulp-sourcemaps": "^2.2.0",
    "jshint": "^2.9.4"
  }
}

*/

var themename = 'themename';

var gulp = require('gulp'),
	autoprefixer = require('autoprefixer'),
	browserSync = require('browser-sync').create(),
	image = require('gulp-image'),
	jshint = require('gulp-jshint'),
	postcss = require('gulp-postcss'),
	sass = require('gulp-sass'),
	sourcemaps = require('gulp-sourcemaps'),

	// Only work with new or updated files
	newer = require('gulp-newer'),

	// Name of working theme folder
	root = '../' + themename + '/',
	scss = root + 'sass/',
	js = root + 'js/',
	img = root + 'images/',
	languages = root + 'languages/';

// CSS via Sass and Autoprefixer
gulp.task('css', function () {
	return gulp.src(scss + '{style.scss}')
		.pipe(sourcemaps.init())
		.pipe(sass({
			outputStyle: 'expanded',
			indentType: 'tab',
			indentWidth: '1'
		}).on('error', sass.logError))
		.pipe(postcss([
			autoprefixer('last 2 versions', '> 1%')
		]))
		.pipe(sourcemaps.write(scss + 'maps'))
		.pipe(gulp.dest(root));
});

// Optimize images through gulp-image
gulp.task('images', function () {
	return gulp.src(img + 'RAW/**/*.{jpg,JPG,png}')
		.pipe(newer(img))
		.pipe(image())
		.pipe(gulp.dest(img));
});

// JavaScript
gulp.task('javascript', function () {
	return gulp.src([js + '*.js'])
		.pipe(jshint())
		.pipe(jshint.reporter('default'))
		.pipe(gulp.dest(js));
});


// Watch everything
gulp.task('watch', function () {
	browserSync.init({
		open: 'external',
		proxy: 'http://localhost:8888/themename',
	});
	gulp.watch([root + '**/*.css', root + '**/*.scss'], ['css']);
	gulp.watch(js + '**/*.js', ['javascript']);
	gulp.watch(img + 'RAW/**/*.{jpg,JPG,png}', ['images']);
	gulp.watch(root + '**/*').on('change', browserSync.reload);
});


// Default task (runs at initiation: gulp --verbose)
gulp.task('default', ['watch']);