PRINCIPLES OF LEADS AGAINST SLAMS
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(i) Take your A only if there is a very likely second trick, other wise
    try to develop a side trick.
    Eg. Against 6S, take your A as you or your partner may develop a S trick
        holding Qxx Axxx xxx xxx OR x   Axxx xxxx xxxx
        But lead a D holding xxx Axx 1098x xxx OR xxx Axxx Qxx xxx
(ii) Against Slam in NT, don't lead 4th best and don't try to develop a 
     trick. Go passive and lead harmless lead, even opponents suit.
     Eg. if S is opponents suit, lead S holding
     xxx Jxxx Qxxxx Jx
(iii) Don't lead singleton against grand slam or 6 NT
(iv) Against slam in a suit, singleton is a good lead
(v) Don't lead A against a slam in NT. Against a suit slam, lead of A 
    is a fair lead, neither good nor bad
(vi) Review the bidding and if it appears that opponents have enough tricks
     in their suits, make an aggressive lead even from a ten-ace to develop
     a trick
(vii) If declarer has shown 2 suiter and hand shows either you or partner
      having length in declarer's second suit, lead trumps to prevent
      ruffs in dummy.