Do not have special feelings/fall in love with your instructor. The negatives outnumber the positives.
If you are planning to compete, it is not how many lessons you've had or how long you've been dancing (Am I good enough to compete?) that will determine when to compete- it is when you decide you really want to do it. You would start in the newcomer division. The competitive spirit doesn't really start until advanced bronze/beginning silver levels. And the most important reasons- fun, fun, fun, and a sense of accomplishment (well deserved). You may want to spectate before you compete.
Go to many social dances. Dance with many partners- not just with your spouse or significant other. Again- have fun.
Do not wear jeans and sneakers to lessons, social dances, or competitions. I feel that this shows disrespect for yourself, your instructor, and your school.