The first thing you should do when starting a scenario (after going through a Road Event when applicable), is look in the scenario book to get the map tiles set up, all the monsters you will be fighting prepared, and apply any scenario effects. Next, you should deal battle goals and choose one. After choosing your battle goals, then you can decided which items you would like to equip from the ones you own (adding in -1 cards to you attack modifier deck when applicable) and which ability cards you would like to start with from the pool of those you have available to you.