What hangs overhead does more for a sukkah than anything on the walls — greenery softening the schach line, and spinners and suncatchers moving and catching the light through the gaps. It is the first layer to put up and the one people notice first.
Hang from the frame, not from the schach — the schach should stay undisturbed, and it will not carry weight in any case. Garlands, vines, spinners and suncatchers all attach easily to the top rails with clips, hooks or cable ties.
Fasten at both ends rather than leaving a strand loose, and hang heavier pieces where they have room to move without hitting anything. Spinners are supposed to turn, so give them clearance — what you are preventing is the strand that whips loose and wraps itself around a light fitting.
High enough that nobody stands into them, which in practice means well above head height for an adult standing up. Over a table, keep the sightline across it clear so people can see each other — decoration that has to be looked around gets moved by the second meal.
Go vertical and keep it light. A few strands along the schach line and one or two suncatchers near an opening fill a small sukkah without closing it in. Skip the large hanging pieces — in a small space they crowd the table rather than decorating it.
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