For Illuminations, we like to stand near Italy - like the pp said there are tons of good places to stand since you can see it from just about anywhere around the lake. If you want a really good place, make a ps at the Rose & Crown for just before the show. Of course, you'll be expected to eat.

You can also grab dinner and a table at the Mexican cafe (Cantina del San Angel), this is counter service so you have to get there early if you want to get a good seat. Of course, it's always a crapshoot because that's a really popular spot. We like to go offseason and when we want a good spot near the railing so we're not standing behind a bunch of people, we find a half hour early is the mininum. DH and I are on the taller side, so even if we do have to stand behind some people we can still see almost everything.
For Wishes we stood near the entrance to Tomorrowland and felt it was a good viewing spot, although I thought a spot along Main street like the pp suggested would have been better. Last time we stood on the path that goes down to the smoking area in front of Tomorrowland (It's that cute little covered area by the water) and we had a terrific view of Tink making her way across the night sky. Very cool.
We also tried to grab a table & chairs at the Plaza Pavilian restaurant patio, (they were redoing the restaurant so it wasn't open at the time) but found if you're not right up against the rail, you really can't see much since it's covered. So you have to get there really early if you want that - but at least you'd have a chair to wait on.
hth!
Cheryl