A gulpfile.js layout i use alot.

gulpfile.js

// Load plugins
var gulp = require('gulp'),
    sass = require('gulp-ruby-sass'),
    autoprefixer = require('gulp-autoprefixer'),
    minifycss = require('gulp-minify-css'),
    jshint = require('gulp-jshint'),
    uglify = require('gulp-uglify'),
    imagemin = require('gulp-imagemin'),
    rename = require('gulp-rename'),
    clean = require('gulp-clean'),
    concat = require('gulp-concat'),
    cache = require('gulp-cache');

// Styles
gulp.task('styles', function() {
  return gulp.src('dev/scss/style.scss')
    .pipe(sass({ style: 'expanded', }))
    .pipe(autoprefixer('last 2 version'))
    .pipe(gulp.dest('assets/css'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(minifycss())
    .pipe(gulp.dest('assets/css'));
});

// Scripts
gulp.task('scripts', function() {
  return gulp.src('dev/js/*.js')
    .pipe(jshint()) //'.jshintrc')
    .pipe(jshint.reporter('default'))
    .pipe(concat('script.js'))
    .pipe(gulp.dest('assets/js'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('assets/js'));
});

// Images
gulp.task('images', function() {
  return gulp.src('dev/images/**/*')
    .pipe(cache(imagemin({ optimizationLevel: 3, progressive: true, interlaced: true })))
    .pipe(gulp.dest('assets/images'));
});

// Clean
gulp.task('clean', function() {
  return gulp.src(['assets/styles', 'assets/scripts', 'assets/images'], {read: false})
    .pipe(clean());
});

// Default task
gulp.task('default', ['styles', 'scripts', 'images']);

// Watch
gulp.task('watch', function() {

  // Watch .scss files
  gulp.watch('dev/scss/**/*.scss', ['styles']);

  // Watch .js files
  gulp.watch('dev/js/*.js', ['scripts']);

  // Watch image files
  gulp.watch('dev/images/**/*', ['images']);
});