Ways to keep your phone charged longer?

I have the iphone 7 plus and i got it about a month ago and it dies pretty fast so i was wondering of some stuff i can do to keep it charged other then low power mode and airplane mode. Or some stuff i can delete in settings that's draining my battery. Any thing will help!

Turning off Bluetooth is a big one. Also turning down your screen brightness helps a lot. You should also get into a habit of constantly closing out of any apps you aren't using. Turning of location services can also help a bit. Also, you need to make sure you are completely draining the battery before you recharge (as often as possible), and taking the phone off the charger when it's full (whenever possible). Smart phones do a horrible job of battery management and it's important to properly charge and discharge your battery. It really can make a huge difference if you just get into the habit of doing it properly. Outside of this (and low power mode like you said) there isn't much more you can do. Smart phone batteries are far from super high capacity pieces of hardware. Battery technology has come pretty far over the years, but you have to keep in mind that smart phone manufacturers are basing their battery capacity on call time and standby time. As soon as you start actually using the "smart" features of the phone such as running apps, web browsing, and watching videos, you can fly through battery life extremely quickly. Just know that it's not just you that has this problem. There's a reason why external battery banks are so popular.

With iphones, the most important thing is to "kill" each app after you close it.
Simply clicking off it leaves it open in the background and some still use CPU power, draining the battery.

Double-click the home button and flick everything off the top of the screen. Do that every time when you finish using it.
Only leave something running in the background if it is required for a specific thing.

I do that but otherwise leave everything turned on - Wi-Fi, Bluetooth, 3G etc.
Like that and with a smartwatch (pebble) permanently connected and it's app left running in the background, I get around 48 hours on my iphone 6, which is something over two years old.

Leave brightness set on "auto", it will adjust to suit light levels.

Note that lithium batteries give longest overall life when _not_ fully cycled between full and empty; somewhere round a 50% span is most practical to give the best overall life, eg running between 30% <> 80%.

That's not practical with a phone where you need maximum life, but putting the phone on charge when it's down to 30% is fine.

You do need to fully charge>fully discharge it occasionally so the "power meter" system can stay in sync with the real condition of the battery, but once a month is fine.
Reference:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Occasionally an app can crash and mess up the power usage; rebooting the phone once a week or so should take care of that.
(Hold the power button until the option to turn off appears, swipe that then wait a couple of minutes and press power again to turn the phone back on).