Hey, I want to up my building skills in minecraft! Do you know simple tips and tricks on how to build better interiors? I am trying to build a modern penthouse.
Sure! I can help with that. There are a number of things to consider when trying to design a better interiors in Minecraft:

1) Look for reference images. Having examples can help with inspiration and drawing from the real world can give a more natural feeling to your projects. 
2) Use lighting to draw focus, add contrast, and create an atmosphere. Warm color lanterns can be used effectively to create a cosy relaxed feeling, while cooler colors create a more energetic effect. 
3) Use decorations and furniture to add more visual interest to the room. Blocks like trap doors, fence posts, and stairs can often be combined to create furniture. Flowers, leaf blocks, and vines can be used to introduce natural elements into the room, which is a key part of modern interior design. 
4) Consider your color scheme. To achieve a minimalist modern look, you should consider lighter muted colours with dark greys and black for contrast. Colors can be used create areas in the room and add visual interest. 
5) Plan where the view lines and focus of the room will be before you build. You should consider where your guests will enter the room from, and what they will see as they do. 

Ultimately how you design your house is up to you. Draw inspiration from both other minecraft builds and the real world, and adopt your favourite elements into your build.