Observe

As you enjoy your beer, make a mental (or written) note of the following:

• Appearance: Is the beer clear or cloudy? Is it pale golden, amber, or even brown? What do you see in the glass?
• Aroma: Swirl your beer gently in the glass and give it a good sniff. What do you smell? Pine? Citrus? Bread? Toast? Fruit? Butter? No need to be pretentious, just make note of what you smell.
• Flavor: What do you taste? 
• Mouthfeel: How does the beer feel in your mouth? Is it watery or full-bodied? Do you perceive a carbonic snap on your tongue, or is it more mellow?
• Overall impression: What do you think of your beer overall? What do you like about it? What don't you like about it? Is it easy-drinking and refreshing, or is it heavy and filling?

You don't need to make this too complex. Just make some observations. Let your impressions guide your next brew day. And the one after that. And then the one after that. Over time, you'll learn how even subtle adjustments to your recipes and processes can influence the beer you brew.

Of course, if you'd rather just kick back and drink your beer, that's fine, too!