Spend time both before and during the meeting getting to know them and the company (assuming this is a commercial client). Way too many reps make it about themselves and what they are selling.
This question is right up Chris Peterson's alley. Also the source of thousands of "How to sell" books. It's also why successful sales people do get paid well. What can you do before you see the prospect? As you alluded to, first you have to see if they really are a prospect or one of you is practicing. Don't take it personal, some companies have their sales people call on others to learn from. Maybe they aren't a good fit and you want some practice? You never know. So, they are a prospect and you want to move forward. There are some things you can do in advance to build credibility. I'd tell you but this is open forum and I'm not training my competition! There is always the facility tour. Let's them talk about the company and on the way you may meet some other decision makers while gathering other potential issues. They speak, you listen. Don't use someone else's design as all you are doing is designating them as the expert and you are "just a bidder" UNLESS it was designed by an outside consultant. Then you have to cautiously make suggestions or the wrath will come. Make commitments in firm time periods. Not next week, Tuesday at 2:00. It matters. It's fair to ask "when will this be needed". "How would you like me to communicate with you" (email/text/phone) "what else could I work with you on, as they may not understand all the opportunities you can do. More to come later.....,
I like to initiate a hand shake (nothing worse than a limp hand) and read how the body language is being transmitted. In all my years of selling the environment albeit commercial or industrial really makes no difference to my approach. A first impression is one of confidence without arrogance that took time for development.
Just think about what annoys you don't act that way and be like others who have left you a good first impression. As mentioned let them do the talking you don't need to toot your horn, that's often is misconstrued to mean many things or for this analogy, sounding like a bragger. I don't think you can "ensure" everything in a meeting that's usually a proving mechanism with time which is worth a mention to prospects. And as ZZ Top sings "nothing looks better than a sharp dressed man" .
If you're not successful ask your potential client how you could have improved your first impression when I ask years ago I was told I talk too much...ugggg