English words can be tricky to spell, as they are not always spelt like they sound. Sometimes you just have to memorise them.
According to the Macmillan Dictionary, these are the 50 most frequently misspelt words in English. These are all commonly used words, so it would be very worthwhile to learn their correct spelling.
The correct spelling is on the right.
accomodation > accommodation
adress > address
accomodate > accommodate
rehersal > rehearsal
commited > committed
persue > pursue
occurence > occurrence
lenght > length
strenght > strength
seperate > separate
appaling > appalling
throught > through
commision > commission
comission > commission
recieve > receive
collegue > colleague
desease > disease
compell > compel
bizzare > bizarre
concious > conscious
advertisment > advertisement
succint > succinct
rythm > rhythm
percieve > perceive
occure > occur
enterpreneur > entrepreneur
aquire > acquire
convinient > convenient
devide > divide
agressive > aggressive
enviroment > environment
supress > suppress
embarassed > embarrassed
miniscule > minuscule
occured > occurred
strech > stretch
embarrased > embarrassed
responsability > responsibility
assesment > assessment
akward > awkward
endevour > endeavour
belive > believe
wierd > weird
achive > achieve
greatful > grateful
biogrophay > biography