Oooo! I love this stuff! Lets start with the most important step.
1. What would make you feel comfortable. Some girls like low key, some fun and playful, others like flashy, and a for others skin is in. There is also any combination of the above. For me, I like to leave a bit to the imagaination. So my clothes are more full coverage.
2. Find an era that you adore. For a lot of girls, modern fashions are the go to. For some it's goth, rock, punk, teen, bohemian, or retro. I personally love everything about the post WWII era. Simple and sexy, leaving a bit to the imagination while presenting a very polished appearance. Granted it will grab attention, but you can take a slightly more modern approach by ditching a crinoline, or leaving out a few of the accessories and it can easily become low key.
3. Body type. Pick your favorite feature and accentuate it. There's no easy way to explain what you need to do. The best way is to try it on and look in the mirror. If you love it... own it. If its just ok, then leave it for another day. If you hate it, then you know what doesn't work for you and you move on.
4. Accessorize. Take the clothes that you like with you when shopping accessories. The ladies at the store will be able to help you match things up. Although bags in stores is somewhat frowned upon, many of the ladies that work there will understand and know that it's required to have the clothes present to properly complete the outfit.
That's all you really need to do, in a nutshell.
Makeup Makeup gets a little more intense, but there are plenty of aestheticians that can knock out a look for you with no effort. It's best to have your daily wear closet figured out and be wearing an common look from your closet when you go to see them. They'll see exactly what you are going for. Sephora is a great starting place for help with makeup because they carry a large variety of cosmetic lines and can mix and match to make it work for you. That will build your base for what works. Then the fun of trying new things to see if anything works better can begin, but only after you have your basic go to's.
I have found no replacement for professional help. Many women have had 20-30 years to evolve and perfect their style. Most trans women are really behind the power curve in that respect. Specialists are handy for accelerating the process.
So what is your fashion goal? What looks excite you?