Dosing will be highly dependent on your desired results and whatever else you have in the mix. Timing I favor upon rising on an empty stomach and then around 6 hours late an hour away from any meal. Additional compounds again depends on what you are after. Clen is a popular partner, I cannot run it myself though.
25mcg twice a day will produce results and this is probably my recommended starting point as well as what I personally have done the most. 50mcg a day is better per se but you best be on some aas with a lot of protein or wasting could occur