A portrait of a loved one can be a variety of sizes, though the larger it is, the more detailed it will be. Ideal spaces for a portrait tattoo would be flat surfaces, again to promote detail, though it is not a requirement. Classic portrait tattoos are done in black and gray, though you can add color if you wish. Keep in mind a life-like portrait tattoo is one of the most difficult styles and should only be trusted to an experienced artist.
If the passed loved one is someone with whom you shared a solid bond, then they more than likely gave you some type of advice. It can be merely a few words or several sentences, though the longer the advice, the larger the tattoo will be. There are hundreds of styles and fonts to choose from when selecting a scripted tattoo, but an even deeper and more personal way would be to write the words in your own handwriting onto a piece of paper and have that image transferred onto your body.
Choose a random object that was significant to you and your passed loved one. It can be anything so long as it carried a unique importance to the both of you. It can be large or small, black and gray or colored and it can be placed most anywhere on your body, although over your heart would be the classic spot.
Initials or dates can be added to any of the tattoo ideas listed above or simply represented on their own. A loved one's initials and life dates can be done in any script, but again, it may carry more significance if you design the font yourself. Small and simple tattoos like this can often be the most meaningful and direct as their is nothing abstract about them.