**Just because Kratom affects the class of morphine related receptors does not mean Kratom or the alkaloids are from the class of 'opiods'. Kratom is NOT an opiod.
Anthimus has explained most of the general knowledge. I'll try to chime in on a few points.
Personally Id probably start with 10 or so grams of leaf. Powder the leaf if it isn't already powderized. Mix it in with a tasty juice of choice. You have to mix for a reasonable amount of time to get it to mix thoroughly and not have all the powder sit on top. The effects usually begin within 5-10 minutes, peak in about 30+/- and go for about 3-5 hours..give or take.
Your alternate method could be a tea, which will hit faster and harder but wont last as long...usually in the range of 3 hours or so. Usually a teas made with two 30 minute simmers, collect both simmers and reduce to a cups worth. Add honey and cinnamon to flavor. (Make sure after each simmer you strain the powder through a coffee filter or cloth.)
I've used kratom for acouple years now and I've found the best method to be the tossnwash/smoothie/juice method. The tea, which having the alkaloids extracted into the water...is VERY bitter and most people dont care for the taste too much. But just mixing the powder in with juice..the bitterness/nasty taste is cut down considerably. The only downside I've found is that it's gritty due to the powder being suspended in the liquid.
If you can handle 10g or theres not too much effect..bump it up acouple grams at a time until your at your desired level.
Kratom is a very underrated plant I feel. It EXCELLENT for pain management...I find moreso than any opiate-derived drug. I've had considerable ankle and lower back pain for about a year now. There are spurts when the pain really affects me on some days, and Kratom is the only thing that will make the pain virtually non existent. Not saying it's like that for everyone, but it's worked wonders for me.