Ha...
He's not very newbie friendly. It's why you often see people say when someone picks Techies, they're either super pro or super fail. You need to be very good at mana management. This means not only do you need to know how to properly calculate and spend your mana, but you also need to know all the mana maximizing tricks such as dropping int items when you activate soul ring or mana potions or bottle.
You also need to be very good at map awareness as that's how you'll be plotting your traps. So you need to know if there's a jungler, and what kind of route the jungler will take. Or what kind of gank paths the enemy will most likely approach you or your team by. You need to know what kind of escape route you'll be using so you can cover it several minutes in advance. Etc. etc. etc.
Lastly, you need to be very aware of how much damage all your skills do because this is a hero where you can't fuck up. If you didn't plant enough mines, all you will do is annoy an enemy and you wasted several minutes of work. If you pressed your suicide too early, you just died for nothing. Things like that. You need to know how to clear creep waves properly with the mine (drop mine, then autoattack every creep once unless they've taken damage prior). You need to know how to stack and pull creep camps so you're not boned when you have no farm.
Your best bet is to practice in bot games until you are completely confident in him. Your goal is not to kill bots, but rather to get used to this very weird hero. Otherwise you're just going to get wrecked nonstop.
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Waga's build is:
Null talisman and tangos -> soul ring -> mana boots -> whatever he feels like
Max mines, then max suicide. Ignore stasis trap until both skills are maxed. Get ult at normal times.
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My preferred skill build is:
Max mines, ignore stasis trap until after I get ulti, then max stasis. Unless I'm playing support, then I'm maxing stasis first.