1/8 is a bit much for a first timer; for many it will be fine (more than fine, in fact), but a bad trip on 1/8 could be hard to break out of for one new to the psychedelic state. 2-2.5g is a good starting dose.

My advice on shrooms and acid: only take them if/when you are absolutely sure you want to, AND you have 6 (shrooms) or 12 (acid) hours of time during which you do not have to get anything done, will not have to interact with anyone you would have to keep your trip a secret from and are in a positive mental state. Also, try not to expect particular things (visuals, ego-annihilation, or any of the other possible elements of a trip); getting frustrated when the desired effect does not happen can hurt the quality of your trip. Be open-minded, be prepared to explore parts of yourself you didn't even know existed, expect nothing and embrace everything... And you'll be in for the ride of your life. Nothing compares to the experience, and no amount of reading on the matter can impart an accurate notion of what it will be like, particularly since it's so wonderfully varied. The only thing that's probably safe to say is that it will be nothing like you imagined.