I. Research your phone and model thoroughly before buying.
One of the trickiest aspects of using an android phone is the process of choosing or shortlisting one before buying. Unlike the apple world where various iPhone and iPad models are shipped by just one seller, the android world is more like a flea-market where multiple sellers like Samsung, HTC, Xiaomi, etc. keep churning out numerous budget models one after another in hopes of making it big. As a user, you must be able to separate wheat from the chaff as its too easy to select the wrong model with known problems or a phone with older android version receiving fewer updates and getting stuck with it.
While its true that the android open source community also keeps helping enthusiasts on support forums like xda-developers, the sheer number of android models means that only the best selling or popular ones will get the community's attention. So, its important to choose a running model to ensure that you get timely updates and community support in future. One of the best ways of doing that is to keep track of forums like xda-developers and ensure that the device you are buying is getting attention there!
II. Learn about basic helpful utilities like hotspot, MTP file transfer, etc.
Even the cheapest of budget android phones these days come with some very basic features which are built into the core AOSP (Android Open Source Project) itself. Some features like basic telephony (calls and text messages), bluetooth, music player, etc. are pretty well known but others like hotspot, MTP file transfer, etc. aren't studied in much depth. You'll be surprised after learning about some of these features. For example, did you know that apart from being able to reuse internet connection, a wifi hotspot can also act as a small home-network so that you can run an FTP server on your android phone and be able to access its files on your PC or laptop connected to that hotspot remotely? In the absence of a USB data cable, this can turn out to be a useful way of transferring files between your phone and another device.
Coming to the topic of MTP file transfers, its painfully slow by default. You can speed up the process by using specialized file-transfer apps on Windows/Mac. If you are a power user who knows how to connect your phone to PC in debug mode, the other option is to use a tool called ADB (Android Debug Bridge) which also has many other uses apart from transferring files.
For learning about similar other utilities built into all android phones and improving your android know-how in general, you might find the below community support forums helpful for reference:
III. Remember to clear the cache often.
Your app cache frequently gets filled with several hundred MBs (or sometimes even a few GBs depending on your usage!). All you have to do is open the system settings, then head over to storage settings and just tap on the stats section showing details of space occupied by cache memory on your android phone. Your phone will be rid of this extra baggage momentarily but you must keep doing it every few days as cache memory keeps getting filled up and starts eating on your internal storage free space.
IV. Be wary of the apps you install from Play Store and the permissions you provide them.
Ever since the beginning, the android app ecosystem has been quite eccentric and eclectic to say the least! Many app vendors are just trying to profit off your private data or show you intrusive adverts. But the ones you need to be truly aware of are apps with malefic intentions (also known as malware). Thankfully, Google usually does a great job of scrutinizing the apps on the Play Store, but you must never let your own guard down too. Especially problematic are those apps which ask for intrusive permissions like access to telephony features (mic/calling/SMS) and account data. You must try to use your judgment here. For example, why should an ebook reader app demand access to telephony features or your Google profile data? Or for that matter, why should a GPS or compass app demand access to storage permissions? If you feel that an app is being too intrusive of permissions, you can try finding a competing alternative which is less so.
Also note that with android version M (and above), apps don't usually ask permissions at the time of installation but when you actually start using the app. Sometimes, the app becomes too persistent and refuse to work unless you provide those permissions! When that happens, the app becomes intrusive. If you still badly want to use that app so much, you can consider giving those permissions but then cut deny it internet access from settings (its possible since Android M and above), so that at least it won't phone home the collected data. If the app cannot work without internet and is also being intrusive, you may try finding a competing alternative. Usually, there are more than a few available.
Finally, there is also the case that more popular an app is, it should be slightly OK to give it more permissions. Popular apps with millions of installs like WhatsApp, Skype, Chrome, Amazon, etc. are typically on the radar of most security experts, so you may install them without worry even if they ask for more permissions.
V. Be wary of the pre-installed apps.
Some vendors like Samsung and Xiaomi are notorious for this, they replace stock android utilities with their own. For example, Xiaomi phones come with Mi File Manager app instead of using the stock one. It also sports apps like Mi Video, Mi Browser, etc. Now, these apps reside on the system partition, so you cannot easily uninstall (or sometimes even disable) them and as a result, you end up with competing apps for the same feature (like Chrome and Mi Browser). If that happens, try to disable the system app if possible. If you are a power user, you can use adb to uninstall them too on some models. This is another reason why habit-1 (online research) is so important. You will come to know of any problematic apps on a phone model before you buy it.
VI. Don't root your phone unless its absolutely necessary.
Rooting is a controversial topic in the android community and you will find proponents who argue on both sides! It was a much needed thing in the earlier days of android versions like ICS (Ice Cream Sandwich) and KitKat when some basic features like granular permissions, firewall, etc. were not available in the stock version and rooting had some benefits. But since android M (and above), most of these additional features already come in the stock version, so there is usually no benefit in rooting. Remember that rooting not only carries some risk of bricking your phone (in case you haven't carefully researched your phone model and its peculiarities) but your manufacturer also typically voids your phone's warranty if its found out that you rooted your phone. Don't do it unless you absolutely have to.
VII. Don't install system updates just because you have to.
When it comes to installing updates on modern gadgets, I like to err on the side of when you are happy, don't try to be happier! Whenever an update is released, don't rush forward to be the first one to install it. If possible, visit the support forum and see if the updates are solving any known issues and more importantly, ensure that they haven't introduced any new issues! More often than not, you'll find many a support forums where users are cursing and repenting after installing an update. Some find the device lacking in performance after the update, others find issues like lagging, an app crashing, etc. Best idea is to wait for some time after the update is released and then only install it if it provides fix for a known problem that's bothering you. Remember, when you are happy, don't try to be happier!