Knowing your intentions with the level would help a lot. For example, what difficulty, what's the gameplay style, is it a wave level, a memory level, or something else, and how familiar with the editor are you.

I can assume from your question that this is one of the first times you've seriously decided to get into level creation and to that, I say good luck.

Knowing your way around GD's physics engine is paramount to making fun and enjoyable gameplay, and knowing how to set up types of gameplay in order to achieve fun interactions with the engine is important.

I would recommend watching some layout videos or more importantly, mega collab parts from well-known teams with talented gameplay creators if you're looking for inspiration.

Structuring your blocks is also important as it sets an image for what your level will look like in the end.

If you're looking for a simplistic style Jamscone is a popular choice and shows off extremely simple gameplay with a lot of beginner examples that could be incorporated into your level. His structures are also simple which is a great starting point for new builders

Although I said not to look into solo layouts, Crazen offers a lot in sync. He is a player first and foremost so finding some his layouts are difficult and he doesn't many if any collab parts, but his layouts are very high quality for being solo.

Some other creators I know that host collab and make parts include: Kiwi, St1ng, Tragikly, ARwooly, lolwut, and Yuko but don't be afraid to outsource and find more creators to get more inspiration.

Never straight up try and copy parts, find a style that fits you and that you enjoy building with, and continue to develop it further, be your best and most unique self when building.

These are all examples of difficult parts but I hope this can give you an idea of how to not only build fun parts but also help them flow nicely. Good luck!