Please make sure that you are regulalry looking at, reading and writing the year 3 and 4 common exception words. There is a PDF which you can print off and use.
See how many times you can include them in your independent writing!
Spelling games for year 3/4 word lists can be found on Spellzone here.
More examples which should be learnt by the end of year 4 can also be found here.