If you really wish to do a spell to boost the probability, there are a few things you can do.
Simple wish spell: Write what you desire on a dried bay leaf, light the leaf on fire (I suggest holding it with tweezers to prevent burning fingers) and visualize the desired outcome.
Take a green candle, rub from the tips to the center with an annointing oil ( Cinnamon works well) In a clockwise motion. While doing this, focus on your wish to get the job. See yourself getting it, having money to spend on the things you need, and any other positive aspects that would come from it. Light the candle on a fire safe tray or candle holder and let it burn down. You could write a chant to go with it, ask for help from a deity or spirit you work with, or anything else you feel would aid in it. Don't forget to thank them for their help if you choose to ask for it.
Also, make sure that you do things to take it off your mind, after you do the spell. Focusing on it too much can bring doubt into play and it is important to believe in your working.