Hello! I am currently a UCR freshmen that is Pre-Business and I just got accepted to UCI as a junior standing today for Public Health! I made this forum in hopes that I could help other high school seniors that may be feeling a little dejected that they did not make it into their dream school and are deciding between community and UCR (or any UC they are not as excited to go to)! I honestly felt like going to UCR and being able to transfer gave me the best option because I got to have this amazing college experience of living in the dorms while also knowing that I could transfer. I also made the decision to transfer out of UCR during May of senior year in hs and I stuck by it all through out!
First things first, if you want to transfer you should start taking action right now, for me I had around 36 units from AP classes and in order to get 90 units I had to take 3 classes at CC the SUMMER BEFORE going into my freshmen year, I also took classes at UCR during their summer program so in total I took 5 classes over the summer. I made sure that my pre-reqs for the major I wanted to get into were finished by my spring quarter. You can use assist.org to see what classes you need to take for your major or even go to the schools website because it will have it on there as well.
Second, I would strongly advise you to keep your GPA as high as possible because it will count against you, there are many people that get in with low GPAs when you look at the stats but you have to remember that those people are most likely CC students because they get priority over UC transfers (CC>UC>CSU>out of state transfers). Also your UC GPA will transfer over!! It will only be in your best interest to keep it as high as possible.
Third, all of your classes will transfer over! Yes UC will obviously accept UC credit from its sister schools, If you are unsure whether or not your units will transfer over email an admissions counselor to the school that you wish to attend and run it by them.
Fourth, do not stress about having the Letter of Reciprocity, which for those of you who do not know is basically saying that you have completed all the GEs at your school and will not be required to complete the requirements of the schools you are transferring too. I did not have mine done, but I am sure it will help you.
Hopefully this was at least a little bit helpful to those who were wondering what to do! Please ask if you have questions and I will do my best to answer as I was in the same position as many of you were 
I need to contact you ASAP! Please, I am going through the same process and I am still unsure. Anyway to contact you? I am unable to PM you my instagram/sc because I am not a Junior Member YET. Thanks!!
@chocobun : what is your UCR GPA to get admitted to UCI as a transfer? This gives students hope if they are not happy with the UC they are in.