Grounds coming off the engine and going to the chassis are often (at least on Fords) those weird braided stainless strap thingies; other ground wires are just regular insulated wires like any other, generally, unless they've been upgraded or over-engineered. Just follow the positive cable off the battery back to wherever it goes (sometimes a power distribution fuseblock) and see if it branches off with any other large cables from there, then trace those to their respective destinations. If you can locate and get your hands on the starter, that and the battery would be my two first places to start checking and cleaning connections, as they tend to be the heaviest-gauge cables on the car and prone to corrosion or burn-through problems.
If any of the wires look burnt, don't go ghetto and just try to wrap some electrical tape around it; replace the cable, clean the connection site thoroughly with a wire brush, and make sure that it's routed so that it's not laying up against anything hot or near anything it would be inclined to ground out against. If there's any thin spots in the cable insulation, current will seek the shortest path and may short out through that location (especially if it's up against something hot or somewhere it might rub through from movement or get pinched).
On most GM starters, they've got two fat posts and one little post. One fat post receives the thick cable from the battery (or power distribution fuseblock, whatever the case), and the other leads into the starter casing, usually a braided copper wire with a crappy bit of insulation wrapped around it - for whatever reason, these often turn brittle with age and crumble, or somehow otherwise get damaged and the exposed wire can corrode, creating all kinds of fun and random headaches. The little post where a thin wire connects (basically an activator wire from the ignition switch) usually won't be a likely source of problems unless something physically damages it (road debris, clumsy mechanics, whatever).
Whatever you do, if you find the battery terminal ends are all nasty and beyond cleaning, don't be cheap/lazy and just try to replace only the end terminals - replace the ENTIRE CABLE. The reason is that corrosion (usually from battery acid or acid vapor) tends to crawl right on up inside the windings of that cable's wire and is pretty much impossible to clean out without stripping off the insulation from the entire length of cable, unwinding the wire, and spraying/brushing it all clean (I've seen cheapskates actually try that, before, when I worked at Autozone). A decent universal battery cable (sold by length and terminal end type) shouldn't run you more than about $15 at the most from any general auto parts shop, unless you spring for one of those goofy overpriced "OEM direct-fit" cables.
Hope this helps.