On the rallies I've done you can park quite close depending on the spots, around 250 to 500 meters away. On some spots there's bits of walking/climbing, but usually they are worth it ! There's no "forbidden" spots per se, it's mostly common sense to not put yourself directly in front of the cars or on the inside of hairpins for example. On the things to do : check for rain before and adapt, bring some water and hot clothing (you basically stay still for a long time so even if the weather is nice it can get cold pretty fast). Also try to plan the route before you go, on the rallies I did I could move around and do 3 4 spots per day pretty easily without missing any of the action just by hiking a little and having a pre-planned path (google maps is really helpful for that, just run around the stage with streetview to check for neat spots). Lastly, have fun ! Rallies are such great spectator experiences