One thing that many people do is put a standard set of phrases in the intentions. This helps to make the intention into a mini-ritual, which has several advantages and a couple of disadvantages. Some of the phrases that I've noticed are "In perfect love and perfect trust," "In an easy and relaxed manner, in its own perfect time, and for the highest good of all," and "of myself I can do nothing." (The last is a very ego-aware statement that puts the ego in the back seat for the purposes of the intention.)
The advantage of this is that, since it is a ritualistic behavior, it puts your mind into a frame of reference where you feel the intention going out or taking form. This is a very powerful tool, because the belief in the intention is as important, or even more so, than the words themselves.
The disadvantage is that people tend to ignore things that they have repeated too often. Instead of thinking of the ritualistic parts of your intention, it gives your mind a moment to wander.
Together with Annie's point above, we can combine these statements to form some more effective phrasing that helps with the beliefs behind the intentions. First, though, saying phrases like "I am a millionaire" tends to throw up red flags in the unconscious, simply because we are not yet millionaires... That hurts our belief in the intention, which tends to be a bad think. If we re-word it to include both "I am" and a term that we're more likely to see as true, then we'll believe it all the more, which helps the intention tremendously.
An example of putting it all together would be "In an easy and relaxed manner, in its own perfect time, for the highest good of all, I am well on my way to becoming a millionaire."