1. Has (s)he made the first move? Like did this person ask for your digits from a manhole while you were walking to Starbucks? Or was there a phone number request after pointless conversation about the insane amount of ugly people in the bar and how you two are the ONLY hot ones there?
2. So the phone number has been provided. And at this point, I'm assuming it wasn't a fake one to the local crisis hotline. (Yeah, I've done that. Quit judging me.) Has (s)he called? Texted? If this is a yes, at this point it should be apparent. They're in to something. Whether it is the need to taste your skin or to get to know your beauty on the inside is still up in the air. Don't rush. Sometimes letting them taste you and move on is the best for you. Don't be upset, thank your Freudian angel for saving your ass.
3. After the first date or five, has communication continued? Or did (s)he commit a total hump and dump? If you fell victim to an H&D, and you're still wondering if they're into you, stop. Please. For the love of god. Your friends are tired of listening to you make excuses for why another meet-up hasn't happened, and frankly, your time is better served practicing the art of underwater basket weaving.
4. Does the communication include random texts about mushy shit? Or is it strictly limited to "I wanna jump your bones?" This is the point where you start to decide where shit is going. All that sentimental crap out of nowhere? Yeah, they want you for more than your O face.
5. Do they pay attention to you by watching what you do, how you socialize, how you interact with others? Or are they spending time in public checking out their reflection in the window or checking out the ass on that über hot bartender? If they're watching you, in tune with you, this is where you start to have fun. Start picking your nose. Lean over like you let out a massive fart. Do something totally unattractive. If they smile and move closer to smell your brand, you've got this shit on lockdown. Take them home right then and ravage them.
Now, this list is nowhere near all inclusive. In fact, I doubt it is even helpful at all. But, for what it's worth, this is what I do. Not that I've had much success at anything lasting more than a few years. But whatever.