Your relationship with a receptionist or assistant begins at the email phase. They’ll often be the ones working with you to schedule the interview, so make sure to use a friendly-but-professional tone in your emails, say thank you, and proofread, proofread, proofread. An email that's too formal (like greeting the assistant as "Ms. Doe" once she's already signed a note as Jane) or too friendly (opening with "Hey girl!!") is going to produce an eye roll or two, and you can bet that if you're email is riddled with typos, your potential employer will find out that you're not as detail-oriented as you claim to be. You should also try to be flexible when scheduling a meeting -- let the person you are meeting with dictate the time and place. Don’t make it difficult for the person scheduling on the other end. If you do, you’ll have made a bad first impression even before you’ve met.
When you arrive at an office for a meeting, greet the receptionist and assistant with a smiling face. Don't distract them with chit-chat while you're waiting unless they engage you first. However, if they end up walking you to a conference room, it's a good idea to make small talk on the way -- if they don't initiate, you can ask a few innocent questions about their day to ease the awkwardness. And if you see them again after a meeting, be sure to let them know that it was nice to meet them and thank them for setting up the meeting.
When you get home, in addition to the thank you note you send to the person you’ve just met with, send a separate email to the assistant or receptionist to thank them for setting up the meeting. Here’s your chance to lock in that good first impression. Even better, you may have an opportunity to create a new relationship if you’re at the same stage in your career as the assistant. If you felt that you had a good rapport with the person who helped schedule a meeting for her boss, you could ask her if she wants to get drinks one evening and continue to build up your network at that company (NOTE: You should only do this after an informational interview, not after a job interview.).
In Hollywood, every interaction counts. Assistants and receptionists are not likely to forget someone who was disrespectful, and they have the power to stop you from working at or with a company. On the other hand, they are likely to remember the person who was exceptionally friendly and kind to them and might even go out of their way to help when the time is right. So be that person. Very little effort and can yield extremely positive results. And besides, it’s the right thing to do.