You're going to have to be a lot more specific than that. What player count? What kinds of vehicles/ weapons? What game types? Competitive? Casual? Basically, what is it you want to make?
Anything really. But for specifics I planning for competitive. I mainly interested in the asymmetric maps and looking for a max player count of 8. A minimum would be 2.
My tip would be to choose one or the other. I'm not sure what real advice to give you other than the obvious: -Balance your map as well as possible (give every power position a counter) and test your map extensively. For asymmetric maps, make positions as unique as possible from each other in terms of geometry and function.
Start here Also, check out other maps and see what others are doing. You might get a sudden burst of inspiration.
Since your question almost relates to every map out there, I'm to give a very general answer that would help you with any map you make. One Word: PRACTICE Seriously, this is the one thing that new level designers fail to consider when they start making their first maps (Even though it's what they want). You can spend hours on the internet looking up on articles (while it's okay) trying to figure out how to become a better designer. When you really need to sit down on your own intiative and try to learn what you want to do. It's what almost everybody here today on Forgehub, did back in Halo 3. If you can, open up the editor some time, don't draw a sketch, tread the waters, get comfortable with the editor, make it your friend. Start breaking down maps, (both in and outside of the Halo franchise) see what designers did and try to figure out why they did it. Overall, have fun with it. Mapping isn't hard, if you love it. Now personnely, I've already seen what kind maps you've posted up on this website. And that is guts man, you have my respect. Your willing to do what most Forgers (even level designers) are scared to do and that is putting yourself out there. That attitude will serve you well when you begin to further refine your skills. Something I should've done a long time ago looking back. Sorry if this post seemed a little long, I get little wordy on these subjects.
You've got a lot of reading to do ForgeWolf. As already stated, you've basically asked us how to make any map at all. This leaves me thinking you're a little inexperienced but you're keen to learn the ins and outs of Forge. I've listed a few guides you should read through. It's all user submitted, and not all of it is 100% true, but it gets you started. A good Forger knows all the techniques to master and knows of most tricks to get a good map, a great Forger utillises both in a unique style personal to them. So take what you need from each of these guides and develop your own skill set personal to your own taste in map design and Halo gameplay. Competitive Map Refinement Guide Avoiding Framerate Issues Stevo spawning method - a little outdated, but it gets you started. Making maps with our Undead hands Invasion: Conceptualization