choose and enable a crosshair

1. open scripts/hudlayout.res and search a crosshair that you want to use
2. change visible from 0 to 1
3. start TF2 and check if it's centered 

-----------------------------------------------------

if the crosshair is not centered:

4. go back to scripts/hudlayout.res and adjust the xpos and ypos values
5. switch back to TF2 and type hud_reloadscheme in console to apply the changes

-----------------------------------------------------

if it's still not centered:

6. go back to scripts/hudlayout.res and adjust the wide and tall values
7. switch back to TF2 and type hud_reloadscheme in console to apply the changes