sexual explicit photos are not allowed on flickr:)
i have some ideas i use:
1) tag your pictures. if you pictured a flower add tags like "flower, flowers, bloom,macro,nature, summer" and so on. so when someone surfs for pictures related to one of the tags your picture will appear on the search!
2) add your pictures to some groups (so called 'pools'). if you've pictured your dog search for pool that is dedicated to dog pictures. you will be astonished how many pools you find. there are many different pools: lip prints photos pool, colorful photos pool, vegan food photos pool and so on and so on :)
3) geotag your pictures. it means you can point the location where you've taken the photo. so when someone on flickr wants to view pictures taken in your location, he/she will see your pictures.
also people like to view pictures that are good in quality, so if some photo is too much blurred better don't upload it.
oh and as someone already said: the more unique and crazy picture is the more attention it gets :)
last but not the least:) leave some comments under pictures uploaded by others!