Check if WooCommerce is active

Most WooCommerce plugins do not need to run unless WooCommerce is already active. You can wrap your plugin in a check to see if WooCommerce is installed:

// Test to see if WooCommerce is active (including network activated).
$plugin_path = trailingslashit( WP_PLUGIN_DIR ) . 'woocommerce/woocommerce.php';

if (
    in_array( $plugin_path, wp_get_active_and_valid_plugins() )
    || in_array( $plugin_path, wp_get_active_network_plugins() )
) {
    // Custom code here. WooCommerce is active, however it has not 
    // necessarily initialized (when that is important, consider
    // using the `woocommerce_init` action).

Note that this check will fail if the WC plugin folder is named anything other than woocommerce.