I followed this order, after the december update my weight skyrocketed (b/c of the troop focus in matchmaking), but fortunately it's back to where it should be:

TESLAS--always recommend for clanmates to get these maxed ASAP. This is just my opinion, but they're my favorite defense, and they carry very low weight.

TRAPS--again, very low weight.

SWEEPERS

--I found 8.5 a waste of time, because I was giving up stars to easily...but I understand it's value. it just wasn't for me--
BUILT New Defenses (WT & X-Bows barred)

BUILT new WT

BUILT X-Bows

Maxed Point Defenses

Maxed ADs
[Upgraded Dark Barracks](witches are ~equal~ in weight to 3 x-bows!)
[Maxed Troops]
Maxed Mortars
[Upgraded to Lego Walls]
Maxed WTs

X-Bows > 2

...and that's where I am now.

Just keep up with your weight, and upgrade in accordance with your attacking ability.

Not sure how accurate these tables are anymore, they're pre-December update, but the values are still precise if you look at them relatively.