My favorite technique (which has worked every time that I've faced karate, kobudo, judo, MMA, tai chi, BJJ, JJJ, kali/escrima, JKD, kendo, kung-fu, ninjutsu, and other stylists) is to enter directly in, offer my right hand and say "Hi, my name's Bronson. I practice aikido and I think what you folks do is really cool, and I'd like to learn more about it" (or some variation thereof)
Bronson