I'm also a Junior member like you and was able to join signature campaign twice already. There is a step by step procedure in every campaign you find in this forum dude. Someone told me that just by staying in this forum you will already  have enough chance of earning. We just need to be patient to attain a higher rank and make a good and relevant posts. Anyway in every Ann thread on a certain project they post there are all the procedures and you can also join facebook and twitter, slack and telegram bounty while you are in a signature campaign. Not much gains in these social medias but better than none.