List the total amount of money you have available to spend at the moment. Note that this includes only disposable income, as you will not want to defer money from rent payments, insurance, or utilities in this analysis. For all intents and purposes, that money is already "spent."
List the number of things that you can purchase with your money. This list shouldn't include everything in the world--keep it limited to things that you can afford and things you actually desire.
Assign each item a numerical value depending upon how important it is to you. For example, if you really want concert tickets, assign it a 10 ranking. If you will only be marginally satisfied with a new smartphone, assign it a 5. If possible, try not to assign the same item the same rating. In other words, do not have more than one item on the list that you consider a 5 or a 7. If you have two items that you consider comparable, try your best to choose one over the other for the ranking system.
Experiment with different purchase combinations, adding up the total amount of "satisfaction points" you receive from each combination. Continue until you have discovered all the possible ways to spend your disposable income. Keep a list of the different combinations and their satisfaction scores. The combination that results in the highest total score is the one that maximizes your utility.