I am looking for a general guide to make better and more complex levels instead of easy ones. If you know any tips, please enlight me! Thanks.
I think the best way to learn is to play lots of levels, especially levels by very good authors. When I first came to the forum, I played all the levels of richardfu. He is one of the best authors (some of his levels are included in the mekorama app). If you are interested, you can find his levels here: https://mekoramaforum.com/media/users/richardfu.16/ and here: https://mekoramaforum.com/media/users/richardfu_.974/ The levels of Master Author are also very good (and maybe a bit easier): https://mekoramaforum.com/media/users/master-author.2652/