step by step using root explorer
move miuiweather.apk to sdcard
open root explorer and navigate to /sdcard
long press on miuiweather.apk and hit COPY
navigate to /system/app
hit menu - PASTE (if it says you can't because its read only, hit the top right button mount r/w, then paste)
longpress on the miuiweather.apk in /system/app
select permissions
make checkboxes look like following: (where x indicates check, 0 indicates unchecked)
Read Write Execute
X ---- X ---- 0
X ---- 0 -----0
X ---- 0 ----0
(all three checkmarks in first column, first checkmark in second column)
same thing with the db file, except instead of /system/app, navigate to /data/data/com.miui.weather/databases/ to paste it
and permissions should look like this
X ---- X ---- 0
X ---- X -----0
0 ---- 0 ----0
you SHOULDNT "install" anything, just move the files to the proper places with proper permissions, and reboot.
i will look into making a flashable zip for each apk if there are still a lot of people having issues