force jQuery to load in the head

Edit: new solution, based on one of the comments. If you are using wp_enqueue_script to load your js file, make sure jQuery is a dependency so that it gets called before your code:

wp_enqueue_script( 'my_script', 'my-script.js', array( 'jquery'), $ver, true );

You can then remove the original enqueue call you had since jQuery will be included automagically