Create a service provider. Thats the best place.

<?php namespace App\Providers;

use Illuminate\Html\HtmlServiceProvider;

class MacroServiceProvider extends HtmlServiceProvider
{
	/**
	 * Register the application services.
	 *
	 * @return void
	 */
	public function register()
	{
        // Macros must be loaded after the HTMLServiceProvider's
        // register method is called. Otherwise, csrf tokens
        // will not be generated
		parent::register();

        // Load macros
        require base_path() . '/path/to/your/macros.php';
	}
}

In addition to the solution provided by @varghesejacob, I'm requiring my macros from the "boot" method because all the service providers have already been loaded by the time this function is run. I have also moved all my macros into a "resources/macros/*" directory because I feel like they belong with all the other view related code.

<?php namespace App\Providers;

use Illuminate\Support\ServiceProvider;

class MacroServiceProvider extends ServiceProvider {

	/**
	 * Bootstrap the application services.
	 *
	 * @return void
	 */
	public function boot()
	{
		require base_path() . '/resources/macros/macro1.php';
		require base_path() . '/resources/macros/macro2.php';
		// etc...
	}
	
	/**
	 * Register any application services.
	 *
	 * @return void
	 */
	public function register()
	{
		//
	}

}

Why just don't add Form::macro into the routes.php

<?php

Form::macro('macros_name', function() {
    ... perform you fucntion here ...
});

* * *

that approach is not save? Or what?

@pavlogagin: sure it's safe, but looks messy and isn't maybe the file you think first of when you're trying to find your macro's in 6 months.