Interior Painting Help

Ive searched the forum before but i still need some help. when you paint the interior do you sand the plastic pieces, if so what grit sand paper. and also what brand primers, and clear coats do you use. ive established that you use krylon indoor/outdoor paint, correct? any help is appreciated because i think i used the wrong paints and clear coats and resulted in a non-drying sticky mess. thanks

i used 600 grit sand paper i think it was

bull dog primer works well....can get it at pep boys

i need help on that too. do some people boil the pieces or something? do you spraypaint them after sanding ? dye them with something else? if anyone has a step by step i could follow that would be great.