Somebody can give me some tips? I'm really bad at this.
I think you should give some background information. What level geometry? What's your math background? Are you in high school, or college, or ? Are you doing self study, or are you preparing for a class? Etc.
Also, these questions belong more properly in the academic guidance forum.
More and longer study time - and studying PROPERLY. Many people learn Geometry (the high school course) in the term, but some people cannot. This is not really the problem that it might seem. The reason is that SOME people are more ALGEBRA people than GEOMETRY people, and in order to deal with Geometry successfully, they just need more time than the single school year (or single semester, if in college).
A few students seem to refuse to follow instructions and do not do enough of the assigned exercises. I'm not suggesting you are one of them; I'm just saying that some students are this way. This is of course, another reason why a few students do poorly in Geometry.
One word: practice. Find a good book, and do exercises. As many as you can find time for.
With Geometry, its great to do the basics with a real model, instead of just numbers.
Actually get some wood or cardboard and string, and measure out the angles, and observe the relationships etc. with a tape measure, protractor, compass and rule etc. get you dad to buy you a cheap laser measurer - none of this will be a waste of time, as the ability to measure will be a fantastic asset whether you become a Scientist, Surveyor or Sanitary Engineer.
Its such fun !!!
Get a sphere (beachball) and mark out the angles, hemispheres, Long and Lat.
Geometry is one of the few area that has a real physical presence, as well as a virtual concept.
Euclid (Father of Gemotry) did a lot of his work on a slate and sand, with a big Compass.
Here's a practical challenge that is huge fun.
Stand on one side of a river, street, canyon etc, and try to figure out how long a bit of string you would need to reach the other side without actually going there.
Hint - Tank Commanders use this principle to know how far away the enemy is.
Separate names with a comma.