A spell is simply a poetic wish for the Divine to do their thing. The key to any good spell is intent. Same for a wish. Focus on your intent while wishing like you do for a formal spell and you should yield a degree of response.
As far as the candle, anything that you can focus on is good. Trying to 'think of nothing' is so hard. The key to easy meditation is having something you can focus entirely on. Plus, by choosing to work with a flame, you may develop the ability to scry with fire.