Paint the picture
Talk about the characteristics that you are looking for in a long-term partner and why. Intentionally choose characteristics that your man possesses, making it clear why you enjoy being with him. "No matter who I am with, they have to have a sense of humor. That's one of the main reasons I love being with you." Not only does this give the man confidence, but also reinforces that you are with him intentionally and not out of blind luck on his part. Men secretly believe that they may not be good enough to KEEP a woman, and so highlighting things that come naturally to him can be a big relief.
After laying the ground work over a period of time, the next step is to tell your man that you have decided that you are done looking. Notice there is no mention of "the man of my dreams," or "the one I want to love forever" etc. Instead, state the FACTS: your mission is complete. This is easily understood and makes a guy feel safe. There is nothing wrong with asking him if he is done looking as well. This is not intimidating to the man because there is no time frame attached to it. It is a simple matter of "do my qualities complete your desired partner?" If he cannot give you an answer to this question you either need to move on with someone else, or ask some follow up questions that will give you an explanation of the uncertainty. Once you have the knowledge that you are the one to complete his mission, it is time to move on to the final step.
Beat the clock
Notice a time frame is the LAST piece of the puzzle. Many women try to make it the first. After you have stated simple facts, laid out your desirable qualities, and both of you have admitted to each other that no more looking need occur, it is FINALLY appropriate to discuss the time frame. This is much easier to do when there is no uncertainty as to whether you adequately measure up. Again, start slow, asking factual questions that require short answers and not long explanations. Avoid questions like, "Describe your dream house." When a woman is asked that question, she will describe every room, curtain, bedspread, and knick knack. When a man is asked that question he might say, "a big one." Help him out by allowing a "paint by numbers" where you supply the picture.
"Would you like to live in the city or the country?" "Are pets a priority for you?" Piece by piece you can get a picture of what his desires are. This strategy works for a timeframe as well. "Do you like Winter or Summer better for a wedding?".
Built slowly and deliberately, this process will help both men and women dance toward the long term together, rather than one feeling led or even dragged down the path. When done correctly, there is an intimacy that comes with the preparation that will last a lifetime.