The contacts app on your phone is the most boring, neglected app ever created. I don't care how much you love your phone -- the only reason you're reading a blog post about contacts right now is because things have gotten out of hand.
Are there people listed in your phone three or four times? Do you have 500 contacts, but only 10 of them have phone numbers? Well, then, it's time to take out the garbage.
The video above has all of my best advice, but I'm going to use this blog post to distill some of the major concepts. To hard-core Android users, some of these things are going to seem very obvious, so bear with me.
I sometimes forget that there are many people with Android phones who aren't actively using a Google account. You technically don't need a Google account to use an Android phone, but most people succumb to the idea of creating an account and associating it with their phone once they have an Android app or game they want to buy. Chances are that you have a Google account associated with your phone. If that's news to you, check the settings menu of your phone and look under the Accounts & Sync menu.
Now, if you head to contacts.google.com and sign in with the same account used on your phone, you'll find that Google has been dutifully synchronizing quite a few of your phone contacts. You'll also find that this synchronization goes both ways. If you add a contact here using your computer, it will be synchronized back on your phone.
Aside from providing a more convenient method for trimming and editing your address book, Google Contacts has a integrated deduping feature. Click the More button and select "Find and merge duplicates" from the menu. This will let you merge all those duplicate listings in one click, or you can be more discriminating by expanding and checking off contacts individually.
Manage your connected accounts
Now that you've cleaned house with your Google Contacts, it's time to troubleshoot the rest of the garbage in your contacts list. One problem I see frequently is that people have multiple types of accounts plugged into their phone, all with overlapping contacts.
In all the excitement of setting up my Android phone, I linked it with two Google accounts, my Yahoo account, Twitter, and Facebook. All of those accounts added people to my contacts list. Personally, I found that deleting my Facebook and Yahoo accounts from my phone led to an immediate reduction in duplicated contacts (I can still use the Facebook and Yahoo apps just fine). So you can trim back some connected accounts if you feel so inclined, but if that's not an option, you can also selectively filter out what accounts display in your contact list using the next technique.
Every Android phone I've seen, from Froyo up through Jelly Bean, includes a settings menu within the contacts app. Unfortunately, every phone seems to organize these settings in a slightly different manner, so it's difficult to offer explicit instructions for navigating them. Here's what to look for within Contacts settings.
Look for a listing of the accounts (and possibly subfolders) that feed into Contacts. Chances are that these will be accompanied by check boxes that allow you to selectively bar accounts from appearing in contacts.
Also look for a setting that allows only contacts with phone numbers to be visible. If I'm on my phone, then I want to call or text you, so an e-mail address isn't worth much to me (but that's just me).
Another way duplicate contacts tend to sneak in is from your SIM card. Chances are that your cell phone's SIM card contains the contacts transferred from your old phone (a practice cell phone salespeople tend to do as a courtesy). I found that the majority of these contacts were either ancient or redundant. It's the reason my mom and dad's numbers are in my phone twice, since they've carried over from every phone I've ever owned. If you want to hide these old SIM contacts, you'll find a check box in your contacts settings to do exactly that.
So there you go, hopefully I've helped solve the mystery of why your Android phone might be displaying so many duplicate or mostly useless contacts. With just a little work, you can make your contact list useful again.