Best of luck! Getting your first job is such a pain. Even the most entry level jobs want experience, which makes it super difficult for people that are just starting out. You're not completely out of luck though! Ask any adults in your life- parents, other family members, teachers you're close to, etc- to read over your CV and give suggestions. Writing CVs and resumes can be tough- there's a reason why some people make a career of writing them for other people. You have nothing to lose by getting ideas about other things you can put in there.
Don't minimise any work you've done previously- if you have babysat kids, that's a huge perk. It shows you're responsible and attentive, and bonus points for minor first aid and feeding kids and stuff like that. Same if you have worked with kids in your schools to do tutoring at any point.
As for places to apply to, this is one of the times when it's worthwhile to just throw as much against the wall as possible. You can apply for positions working with photoshop, but it's unlikely you would be considered for those. If you're really interested, you should look into some classes. Hit up every retail place you can find though- A lot of bigger chain places have online applications, which makes things really easy. No longer do you have to spend hours going from place to place. (Personally, I've always had luck with grocery stores, and they tend to pay quite well, are often in unions, etc. The major downfall is how ugly the uniforms always are). As said already, if you have a strong preference for clothing stores, make sure you show that on your resume. Talk about your interest in fashion.
Interviews are pretty terrifying, but unless you're really unlucky, your interviewer is going to try to put you at ease. They'll ask you questions about why you want to work there, and a lot of general kind of getting to know you questions. At the level you're at, they just want to get an idea of who you are, how you will fit in, and what your work ethic will probably be. You can google common interview questions, but many of them are for higher level positions, and may just end up worrying you!
There tends to always be questions about something you found difficult and how you worked around it, or dealt with it, situations where you had to work with someone who was difficult or you didn't like, something you consider a flaw, etc. Never (ever ever ever!) actually say anything bad about yourself. Talk about a flaw you used to have, but have taken steps to rectify (ie, I used to have a lot of problems getting to school or other lessons on time. I would wake up with only ten minutes before I had to leave, and I would rush around trying to get everything together in time. Since then though, I have started preparing everything I need for the next day right after I get home, and I haven't had to rush since!) or a flaw that's not really a flaw, or not much of one (ie, I sometimes take too long working on a project because I want to make sure that it is the absolute best quality that it can be).
As for clothing, I have always dressed quite smartly in interviews. I tend to be dressed more professionally than the people interviewing me, but I feel better going in that at the very least my outfit won't be the reason I didn't get hired. A pair of black dress pants, and a simple button down shirt or other nice blouse is simple, not too dressy, but looks smart and professional, and is sure to make a good impression. If you do get an interview at a clothing store, it would be smart to wear some items of clothing from that store, but still try to make it as smart as possible. Even if they sell ripped jeans and club wear, it may not be the best to show up at the interview in that clothing- maybe pick some accessories from that store, or a similar store, with accents that show you know (and like) their style of clothing, but that you're classing it up.
Sorry if this is just a big wall of text. There is so much advice floating around about how to get jobs, and a lot of it is contradictory. It may take some time to get a job, especially since the economy isn't the best, but you will get one. :) Make sure your CV is the best it can be (without falsifying anything), and practice some interview questions, and you'll be grand. :)