I was told that when the oleh receives an aliyah he must have his sleeves covering up to his forearm and must be wearing pants. Also, the collar bone cannot be seen. This was derived from something about a grasshopper/cricket who's wings cover the shin bone and forearm. (Anyone have a source?)
Potential olim must be wearing 'Shabbat appropriate' attire. And if what they're wearing is 'not as good' as what they've warn for Shabbat in past (i.e. one shabbat its a suit and then another time jeans), they are not allowed to get an aliyah. (Side note: I have heard of people receiving an aliyah despite their dress, but I'm not sure if those were non-Orthodox shuls)
(hopefully still relevant) All attendees, honorees and olim when within the domain of the Aron Kodesh must wear two head coverings (typically kippa and tallit gadol) during public Torah reading.
Please source if possible. Feel free to mention any books/articles that are Torah Service focused, though I presume I'll have to post this as a separate question. Thanks for your time!