If you would like to lifeguard, teach swim lessons or cashier at a neighborhood pool, make sure you get your certifications well before-hand! Technical issues can pop up any time and could delay your start date or even opportunity to work over summer. I recommend if you want to work over summer, make sure to have everything (including certifications if you need them) ready by February/March. Apply early, see your employers face-to-face, be excited to be involved. Be punctual, willing to learn and fixing mistakes and have a positive attitude.