shiv ling is more powerful than any yantra and tantra. worship shiva in various ways such as abhishekam, rudrabhishekam, rudra yagam, chandi yagam etc. and you will certainly get what you want . these yantra-tantras distract the devotees from main line. if you ask the shiva directly, what you want, he will give you directly. if you ask him through yantra-tantra he gives you through yantra-tantra which is less effective.
about direction of shiv ling, plz see that you face towards east and shiv-ling is facing you and its extension(panapattam/base ) is looking towards north.
always have shiva in your "chit" and try avoiding other ways.