Thinning shears(or thinning scissors as I like to call them) should be used to thin out your hair. I suggest Massugu thinning scissors as these scissors have been designed specifically with the beginning hairdresser in mind. These are simply gap-toothed scissors that cut only half the hair. These also come with various gap sizes, depending on what you need cut away.
I've seen how many people struggle with thick hair and I can just imagine the pain it is to manage it, hope this helps.