The first thing to remember is that a cat or kitten is not a small dog. Kittens especially are typically high energy, silly, and somewhat messy little fur balls. Like children, they will often test their limits and make things into toys that you couldn't imagine they would want to play with (poop hockey is a favorite kitten game.)
If your kitten beings to chew/nibble/bite or scratch you, this is usually a sign of a kitten that is too stimulated/ excited. Do not allow the kitten to continue this behavior. You can scruff the kitten and lift it away from you, or give the kitten a temporary time out in a bathroom (make sure it has a litter box with it!) If that doesn't stop the behavior, just leave the area and ignore the kitten. Also, do not play too roughly with the kitten or cat, as this encourages them to play roughly back.
Items like string or yarn are NOT appropriate toys for kittens or cats and should never be where the cat or kitten could get to them. These are strangling hazards; additionally, if swallowed, these can potentially cause intestinal blockage or torsion, leading to extremely expensive surgery that may or may not save the life of the cat. Consider every toy you purchase for its potential to be swallowed or consumed. Tinsel type toys are also a problem. Under supervision, these toys can be used, but they should not be left out. Practice golf balls are a very safe toy that can be left with the kittens.
Cords and cords for blinds are very tempting for kittens and cats to chew one. Sometimes, "bitter apple" or other type products can be placed on the cords to prevent the cats from wanting to chew on them, but some cats actually seem to like the taste or bitter apple, so watch them carefully. A squirt bottle with water can be used to deter cats from chewing on cords (but you have to be watching them closely to catch them in the act.) Also, a squirt bottle can be used to deter cats from getting up on counters or other areas you prefer they not go.
Also certain plants and essential oils can be deadly to cats/kittens so make sure to do some research on the plants and diffusers you are using. As well as cleaning products. I created an FAQ just on harmful items like plants household goods and foods please look here