Flip your board over so the base is facing upwards.
Get some base cleaner and spray on to an old rag. Wipe down the base of your board. This will clean off any dirt and even grease left behind from man made snow.
If you know when and where you will be boarding, you can find a specific temperature wax. Otherise, just use a universal temperature wax.
Using a wax specific iron, melt the wax with the iron using the least amount needed to cover the majority of the board.