Things to consider when planning a dinner for a partner should include whether or not the meal is going to be a surprise, the venue's location, and what's on the menu. When considering these things, your spouse or partner's reaction should be at the front of your mind.
Consider the surprise factor of the meal. If you're aware that you partner doesn't like to be unaware of plans, schedule a date for the dinner, and make sure that any outside factors are taken care of, such as work or children. If the meal is taking place at one of your houses, make sure that the atmosphere is ready for romance. This includes flowers, lighting, and other points of romantic ambiance like the smell and visuals of the meal. Other details to consider are your clothes, your partner's allergies and potential time constraints.
Only choose menu items that the two of you like, favoring the tastes of your partner. Include a special surprise as part of the meal, such as further plans, jewelry, or anything else your partner would appreciate as a special gift. It's important to consider any activities after the meal as only planning one event or activity like a simple dinner may not be perceived as romantic.