Advice: Have an honest conversation with a potential reference.
Why: Ask first. Don’t assume the answer will be yes, and don’t be offended if it’s not. There are many reasons someone may decline serving as a reference. Discuss your opportunities and make sure they actually endorse all the things to which you’re applying, and find out what the recommender actually thinks of you. Make sure your recommender has a complete picture of you. If it’s been a couple months since you worked with the individual, offer a sample of your recent work. Provide a resume. Use the opportunity to let the recommender get to know you even better. Don’t assume that just because someone’s willing to be your reference that they’ll recommend you for anything. In general, a strong recommendation from an unknown entity far outweighs a weak or even lukewarm recommendation from a person of clout. Finally, find out how the recommender wishes to be addressed on the portions of any form you need to fill out, and what contact information they’d like to have listed. Also, make sure you spell their name correctly!