Spelling

First of all, spelling is really important for an essay. However, there are some words that has same spelling, but wrong meaning. These words are really hard to fix for spell-checkers.For example;
-Their moving here to be our neighbour. ( They`re)

Also, the relation between "ie" and "ei" is quite easy. If the word sound long "e" write "i" before "e". Plus, if there is "c" before that part it`s always "ei" such as:
"ei"
deceive, perceive, receipt, receive
"ie"
hygiene, patience, pierce, priest

Next, it is really common to use -ing, -ed, ‑es, ‑er, and -est. in English.
For example,

Cry – cried – crier- crying

Dry – dried – drier-drying