I have an interview for an entry level admin assistant trainee position either in the next for days or next week. I have no clue what to wear!
Has anyone had experience as an admin assistant or similar position? Any tips or suggestions would be appreciated. I haven't worked outside of the home for about 2 years so I'm a bit nervous.

It's always good to err on the side of caution. Once you get there, you may see that their dress policy is "business casual", but it's best to wear a suit, or a conservative skirt and blouse to an interview. A dress is OK, too, preferably something relatively conservative (not too short, no spaghetti straps, etc).
As an admin asst, they'll be looking for someone confident, friendly, that can work well with everyone in the office. (Many times they'll overlook any skills you don't have, as they can train you, in favor of a personality type that they think will "fit".) Smile when you meet the interviewer, give a firm handshake, and have an attitude of "of course I can handle this job."
Best of luck to you!!
I suggest wearing either dark (navy, grey, black, brown) slacks with a button up blouse in a muted color, a suit (no bright colors), or a skirt that comes to the knee, pantyhose, and shoes that are not too high and have a closed toe & heel. Maybe a pastel top to offset the dark skirt/pants/suit.