After teaching the single sounds of reading there are 44 two letter sounds that children need to become familiar with to become fluent readers and writers.
I have used one sound a day in my classroom. I have had enormous results using these sounds and have always had high reading and writing results.
These can be used as flashcards. As you introduce a sound on a daily basis you add it to the pile of the ones children have learned and revise daily.
If you just taught 3 sounds a week from this collection your children are guaranteed to have the best reading, spelling and writing results.