Not much going on on the lake, the river is where it is at. If you can read the river you'll be fine. If not, just follow someone in a bigger boat that looks like they know what they are doing. I don't know what the flow is right now and that plays a part in how much 'hittable' bottom there is.
From below Fisher's on up there'll be sand bars. I haven't been out this year, but the last 8-10 years there's been a gnarly sand bar right in front of the enterance to Martinez. You just hang a hard right and cruise up the side of it.
You'll find that you are either on one side or the other of the channel all the way up river for quite a ways. All through the north run near lake Fergueson (sp?) the sand bars are in the middle. Sometime's I'll switch sides if something doesn't look right, but if you hug the side you should make it through either side on that stretch. Past the island on the way to Picacho you'll find the sand bars will sometimes be on one side or the other. I've run a couple of jet ski's a pontoon and 2 jets on that part of the river for a while and never got stuck. The only time I've seen a anyone get stuck is when the driver wasn't paying attention. (I was on a daycruiser one time when that happened, man that hurt)
Up towards Walter's there is supposed to be an unmarked rock that'll eat a drive, but I've never seen it.
Downriver from Martinez/Fisher's it is a little easier, but basically I think the whole river is pretty easy to navigate. You just need to watch for the signs. I always suggest staying towards the outside of a bend as much as is practical, since the sand tends to build up on the inside and you can see further anyways.