It's good to start small.
In terms of coming out:
Do you have a best friend? Do you have a good friend of the gender you identify as? Start by feeling it out with them. Like, maybe mention something about the anti-transgender laws that politicians are trying to get passed right now. See what they say. If they react positively, talk to them about what you've been going through. Make sure that they know how big of a deal it is if your secret gets out too soon.
For me, I started coming out last January and next month I'll be out at work, the last part of my life where I'm not out. I came out to various friends individually. I essentially ranked them in order of how important they are in my life and how well I expected them to take it. For some, there was a deliberate disclosure. With others, I just showed up dressed to the nines and acted like I expected everybody to treat me the same as they did the day before. They did. Transfeminine folk have a bit of an edge on this one... wearing a skirt or dress really sends a message, in a way that wearing traditionally male clothing really doesn't.
In terms of being comfortable:
Start small here, too! As I came out, I "drifted" out of the closet. I gradually incorporated increasingly feminine bits into my wardrobe; starting with capri pants, cardigans, painting my nails, long t-shirts... as I started combining a few of those elements in an outfit, people started to notice. Since it was very gradual, I didn't get many comments. Now... I'm saying this as an adult who came out at a university as a graduate student. If you're still in grade school, I'm sure your experience will be different.
By going slowly, both in how you present and who you tell, you can avoid a lot of the embarrassment that one typically imagines. Maybe it's easier going the other way... but if I just started dressing feminine the day I realized that I was transgender, I'd have made a damned fool of myself. Feminine clothes are hard! I kinda knew what I was doing... but oh man, looking back at some of my outfits... yikes.