How would I make this more secure?

[Kryllster]

Here is my code:

 

<?php
// Define form variables and checks

$message = "Please do NOT leave any fields empty Thank You!!";
// Start the process of creation
	$skillname = $_POST['skillname'];
	$class = $_POST['class'];
	$type = $_POST['type'];
	$description = $_POST['description'];
	$name = $_POST['name'];

if (
    empty($_POST['skillname']) ||
    empty($_POST['class']) ||
    empty($_POST['type']) ||
    empty($_POST['description']) ||
    empty($_POST['name'])
  ) {
    echo $message;
    exit();
  }

// connection to database info here
include('../database/dbconn.php');

// Test for duplicate Username. If True then back to form. If not continue.
$sql = "select * from $tbl_name where skillname='" . $_POST['skillname'] . "'"; 
$result = mysql_query($sql);
if (mysql_num_rows($result) >= 1) { 
	echo "That Skillname is already taken please choose another!";
	exit();
	}

	else{
// Populate table from form and defined info
mysql_query("INSERT INTO $tbl_name (skillname, class, type, description, name) Values ('$skillname','$class','$type','$description','$name')");
}
// Direct on Creation Success
header("Location:skillsuccess.html");
?>

 

 

Any hints, tips or direction is appreciated.