Talk is cheap, and telling your partner that she's a priority in your life when your actions don't back up your words is futile. If you want to send the message that you value her above all else, examine your life to ensure that your words are true. Bringing your values into alignment with reality will enrich your relationship.
Time
One of the most valuable resources you have is your time. If you want the person you love to feel as though he is a priority in your life, you need to manage your time in a manner that sends this message. For example, if you spend every weekend shopping with your friends rather than doing activities with your partner, he'll get the message that you value your friends more than him. Be intentional about adjusting your schedule to spend time with your beloved, adding blocks of time devoted to him to your calendar if need be.
Money
Money talks, and nowhere is its voice louder than in relationships. If you put buying an telephoto lens for your camera above taking her away for the weekend, then it is evident where your priorities lie. She will get the message loud and clear. You don't need to allow your partner's needs to bankrupt you, but do take them into consideration when making financial decisions.
Selflessness
Prioritizing someone doesn't just mean spending time and money on them and putting them above others -- it also means that you put their needs above your own. "Psychology Today" columnist Rita Watson notes in an April 2013 article that keeping anger in check is a powerful way of showing love to your partner. Another way is to show kindness and thoughtfulness, such as offering to do the dishes or agreeing to let him use the new car because his commute is so long.
Know the Person
Get to know what makes the person feel loved and prioritized. You can try your hardest to make a person feel as though she is number one in your life, but if you don't know her love language, your message might not get through. In "The 5 Love Languages: The Secret to Love That Lasts," Gary Chapman identifies the following as possible "languages" that your loved one may respond to: words of affirmation, acts of services, affection, quality time and gifts. Pay attention to the language your partner responds to so that your actions will have the maximum positive effect on your relationship.