hola Fernando,
First narrow what subjects fascinate you the most the shop around and all you local Hobby/Craft shops. Something will eventually jump out at you if not several at once. Decisions Decisions. Once you''ve narrowed down you choices. Check the skill level on the box itself. When i first started I did a Skill 2.
If this is you first model you might want to stick with revell or AMT. One of the more popular brands because they have very detailed directions. Some kits manuals don't say what a part is or their picture diagrams are very vaque and hard to read. Just remember this is for fun and personal accomplishment. My first two models I built i did to familiarize myself with how the whole process works and what difficulties I might encounter. So play around abit and enjoy.
Also a good basic tip is to test fit all parts before glueing just to make sure the parts are aligned and won't need any modifications such as sanding or realignments. the more the merry so jump aboard my friend.
Take Care