Get right to the point. If you're hoping to make plans or move forward then just attach it with your initial greeting. It's better to be assertive (but not forceful.) Avoid the 7 wasted texts of back and forth drivel that usually consists of "hey, hey, how are you?, good you?, good, what you doing?, nothing you?" That path to nowhere can take an hour or more, by itself in some cases.
There are alot of people who just don't like to text. Either because they prefer actually speaking, are too lazy to type back and forth, or really just can't be bothered. So because of that, go right in. No point trying to be suave over text when more often than not it does more damage than good due to mis-understanding/mis-communication. Oh, and don't redline. That'll easily fry your sale before it gets anywhere important.