First of all things that help are.

1. Shading posstive ( lighter ) and negative (Darker ).. Which is by pressing "e" on the colorfull bar of saturation ( the bottom ).. Press "Add Color To Palette. NOTE: PLEASE USE A BIG STRUCTURE!

2. Sturcturing like by giving it Ctr +N, Ctrl + M or both of those to make your guns!

3. Follow the rules of NOT GOING TOO BIG! By modifying the size with the bar when your finished...

4. Picture to Outline for a gun structure ( I can't explain it I am using the site's thread for this explaining )
http://www.exatogames.com/forums/index.php?threads/advanced-gun-making-tutorial.3223/

5. Make Ironsights ( I have never done this since I am the melee and explosive workshopper and Thread for better explaining and ) NOTE: USE PAINT.NET, GIMP, OR PHOTOSHOP!
http://www.exatogames.com/forums/index.php?threads/the-generic-ironsight-thread.2542/

6. Saturate your guns.... Ok this is a little bit helpful for unique colors..... Since we got darken and lighten.... Saturating guns lightens them by scrolling the mouse cursor across the color pad. Or use this ( I got this from a thread from mine on the Exato site http://www.rapidtables.com/convert/color/hsv-to-rgb.htm

7. Increase the size of the gun as possible.... It's hard but great details and such. Touch with shading or saturating, or color change ( gradient )

8. Plaster Modeling: ( Imaganation to blocks ) which when you use your brain and imaganation to create a blade or gun. With the most detail and color as possible...

9. Color Changes. Yes this is gradient like by scrolling the going in the color pad with "e" and make it slowly go towards a certain color value...

10. Inspirational Images and Things: By going into google images ( any site that has pictures of things ) and trying to recreate, remaster, and make something out of it.

11. Do not use 1 block...

12. Try not to interfere with other modern games direct cloning ( Like A.O.S * I am certainly not gonna say it over being the closest game to Guncraft )

13. Get inspired by a friend.

14. Try certainly! Not copy players work! Which that is a rule by the way.

15. Build off what happens to your guns in the past. Though my first gun was rejected... I build off of that when the first time I got it accepted..

16. Read the build controlls by pressing Esc -> Settings -> Build Controls