#1. Passion- If you're in the clothing industry for money then just stop here and turn back and leave. If you find the lowest cost for everything and want the most profit then you won't be very successful. Passion is what helps create unique create designs and takes criticism from their customers.
#2. Name- I guess every one here by now knows that they need a unique name. Please stay away from create a name from 2 different names that are popular. Ex. Supremely Dope. Try something that has a meaning because it connects to customers and if it doesn't have meaning to you go back to #1
#3. Brand Type- What type of brand are you are what type of customers are you targeting? This means everything in the world. If you were supreme and you targeted, 40-50 year olds living in beverly hills I can guarantee you the brand would be terrible. This is the most critical because this is what tells you what type of logo you want, what type of website to get, what type of sponsors, models, etc.. If you can't find your niche than you're just a bird flying forever with no where to stop.
#4. Logo- Now since you got #2 and #3 figured out, its time to do one of the most critical things ever. Brand Representation is hella of a thing. Its like even if you didn't know nike, but you saw the check mark you would know who it was. This is critical because this is how you get your clothing brand out there and get FREE advertisement for other people wearing YOUR brand. PLEASE, I am begging you not to do this by yourself if you don't know what to do and can't create a unique logo that represents your brand. Do not do this is paint or have a simple Arial Font Logo. Hire someone. Would you want to deliver your wives baby by yourself? No you want someone else like a professional to do it, but you still get to help and say what to do.
#5. Social Marketing- Brands are made and spread by friends to friends which increases the number of people that know about you're brand. Create a professional website and make it appeal to your brand type(#3). First thing is create a website, please have something on the website. It is such a turnoff when you see a good brand with good clothes then you go to their website and it looks sketchy as hell and nothing looks good and its hard to use and figure out how to do anything. I am not saying spend $500 to create a custom website and whatnot. I am asking you to look for what website you are going to setup your brand at. (shopify, bigcommerce, magento, wordpress, etc.. just google online ecommerce) and look for templates for these websites.
(will add to this but i have a broken arm and i need a break. lol)