A tallis made of leather (that has no weave) is exempt from tsitsis. (MB11)
Clothing split from the bottom to more than halfway to the top and forming four corners are obligated in tsitsis. If there is an arm sleeve – measure to the top of the sleeve. (ShA7)
Tsitsis hung up on a begged which is not chayav is a massui on Shabbos. Do not wear it out to Reshus Horabbim. (ShA 7 – MB 27)
The corners must be square and not round (looking). (ShA9)
Clothing that are meant to mainly cover the head and/or neck and/or shoulders only, are exempt from tsitsis. (ShA10,11)
The atarra is meant to indicate which way is up – so that the upper tsitsis should not switch to the bottom. (MB 33)
The Rama writes that clothing that have four corners but not made in a way that two are hanging in front and two hanging in the back are exempt from tsitsis. Since this halacha is loose in the hands of the geonim, a yoray shomayim should round off one corner (Rama12 – MB36)
A tallis godol should be worn so that the left arm separates between the left two corners at mid-width of the tallis and the right arm likewise, separates between the right two corners. This way you’ll have two corners in front and two in the back while the tallis covers your torso. (MB37)