What should I do in order to keep reject ratio lower? I'm constantly getting about 3% which is quite a lot from what I read here...
Ping to ltcmine.ru from my miner is about 28-30ms which is really nice, so that shouldn't be a problem. What else can keep my reject ratio that high?
Which type of rejects do you get? Is it "unknown-work" or something another?
yes, unknown-work
There are two working sets - pool's working set and miner's local working set. The "unknown-work" message means that work doesn't exist in pool's working set anymore (or never existed). Pool working set cleanup procedure launched for every new block, received by pool from p2p network. Local working set cleared when miner receives "New work found" message from pool.
So, if miner got reject with "unknown-work" message, this means that local working set wasn't updated properly while pool's working set updated already. This could be caused by network problem, and can be resolved by manual expiry time decreasing. Try -E 30 option for cgminer/bfgminer.
P.S. Minimum shares difficulty border now is fixed at x64.