My advice, don't mine random areas. It's a feeding strategy that'll have you under level and under farmed all game. Only when fighting complete noobs will mining that way do much ...as wards will ruin your surprise set ups every time.
Use your ulti as free wards, and go to their jungle with tangos and clear a tree near neutral spawn points and place mines there. Techies real strategy is getting some nice mines down before combat, and using mines as free wards. In combat, stasis is your key skill, imba 5 second stun=sexy, works incredibly well with decent initiators and or kunkka.
For items, I'd suggest going for cheap and easy to complete items. Phase/Bracers/Nulls and throw in a void stone. That would essentially be your core items. If the fates are merciful, you might one day end up with guinsoo, although I'd be tempted to pick up an easier to build, team friendly, item, like necrobook/Mek/Force staff (force staff sounds like fun). I'd almost be tempted to pick up blademail, as techies is usually a free and quick kill; people will be after you, and it makes for interesting, run in with pipe buff, absorb a bunch of AoE with blademail on, and then suicide, tactics. If you are somehow able to farm well early, blink dagger might not be bad at all.
Techies have some interesting strategies, including denying the enemy neutrals. He can also neutral fairly well. His traps can make enemies weary of chasing and pushing.
Techies will never be an amazing farmer, and you shouldn't be stealing your carries farm anyways...but his mines do allow him for decent burst farming, making him a good candidate for midgame support items.
Techies work quite well with heroes like mirana and tree, as they both have long stuns and can both make him invisible, which is nice for placing stasis in battle and getting them to actually trigger. Also, other special mentions include VS and pudge, for obvious reasons, Enigma and alchemist, for the very long stuns.