This is for anyone coming to ask questions that everyone asks, and for those questions people never ask.
This year, we are facing a lot of snow. You can get wilderness permits reserved but you may find snow even in early August in the high country, and there will be plenty of snowmelt in the streams in May, June and even July. Which makes the number one risk to you that rushing, flooding water -- do not use ropes! if the water is deep, fast, you can't see the bottom, above your knees -- TURN AROUND. Beware skinny or unstable logs and rocks! The safest way to cross is WITH BOOTS ON when you can't see the bottom.
Do not use ropes. Do not use ropes. DO NOT USE ROPES. You think it's a good idea to fasten yourself to something so you can pull yourself out. The rushing water is much stronger than you are. You will be pulled under the water, faced with the choice of staying there pushed under by the incredible force that is flowing water or letting go and dying as you are swept downstream and smashed into rocks. Ropes increase risk. Do not use ropes that are tied across the stream, either. Same problem. Don't even think about it. Your backpacking trip is not worth dying for.
http://sectionhiker.com/safety-tips-for ... d-streams/
BEWARE snow bridges. Snow in the melt process will be melting out from the underside -- what looks like a five foot drift might be a foot of snow with a lot of airspace under it, and falling through into icy cold melted snow is likely. If you hear but can't see running water, you're probably walking over the water. Walking on snow over a stream is VERY DANGEROUS. You will become hypothermic in minutes in very cold water.
The top killers in Yosemite are water, and rocks. Be careful of them. Your own health issues are another top killer. Stay hydrated and warm and dry.
Read the food storage pages on the website, nps.gov/yose and follow the rules regarding bears. Bear spray is illegal here. You do not need it. Animals aren't killing people here. Watch where you walk (rattlesnakes are easy to avoid that way) and keep your distance/scare away the furry creatures, from chipmunks to bears, regardless of how unafraid they are of you do them the favor of driving them away. Your food is bad for them. Don't feed or encourage them. Rodents carry hantavirus, ticks (Lyme and other diseases are tick borne) and fleas. Bears will steal food, in some areas of the park they are brave enough to run out and grab something when you turn your back on it -- follow the rules and that won't happen.
Don't trust your life to electronic devices. Leave an itinerary with someone at home. reconn.org is a great template. There are lots of rescues thanks to SPOT, but there are also lots of occasions you never hear about where the device failed to work as advertised -- rangers in national parks and forests will tell you to always leave an itinerary and carry a map because GPS and PLB type devices WILL FAIL for various reasons. User error, device malfunction, dead batteries, glitches in the satellite system, poor signal, or having the device vanish into a boulder field when you drop it or get left on a rock in camp one morning -- these things happen. ALWAYS leave a detailed itinerary regardless of how far you go or what you have with you.