I'm pretty new to this game as well, but I have a couple rules of thumb I use in making up players:
1) Depending on the ratings scale (20-80, 1-250, 1-10, etc.), I use the midway point of those ratings to describe bench players. Anything above designates above-average or better. On a 20-80 scale, very few players get a 80 in anything. Baseball America has a little writeup about who they feel has 80 tools, just to give you an idea:
BaseballAmerica.com: Prospects: Ask BA
2) Even perennial All-Stars rarely have 80 tools in my world. Usually, they have above-average tools in most, if not all, categories. The true 5-tools prospects rarely have 80 tools, as well.