This is how I might do it. https://www.grimtools.com/calc/0V0Pmd9V
Although of course you need better gear. Have a look at the devotion tree.
First off you need to focus on one damage type either fire or lightning in this case. Reason is devotions tend to support one or the other. Some support both but for lightning you take a very different devotion path to the one I gave you.
Temper and vindictive flame get rid of those they are not doing much for you. Vindictive flame might be good later on when you have your final gear and need more attack speed. That’s the only thing that skill is usefull for.
Demon Fire is useless. Blackwater cocktail is ok but take the modifier for - enemy damage it will help you survive more.
In the Shaman Tree - Stormcallers pact is still good for the 35% crit damage I guess. Definitely get 1 point in wind devil and try to max raging tempest. It’s amazing for any elemental build. Wendigo totem you don’t really need. Try to get a seal of blades or some other adcth component. This will help your healing tremendously
Flashbangs - great skill but if your sinking 14 points into it get the modifier and put at least 2-3 points for the fumble chance. When you get better gear these are often one point wonders + skills can boost them to sufficient levels
Devotion wise: Aetherfire sucks for fire builds get fiend it is way better as a left click main attack skill proc. Wraith?? get rid of that as well.
Behemoth: you think it’s good, but it’s really really terrible. Cooldown is too long and it procs randomly - not as a circuit breaker. It will proc when you are at 90% HP heal you up only 10% and then you have to wait for 30 seconds where it provides only a marginal benefit in HP regen several hundred per second. Whereas if you rely on adcth and have enough damage you can steal thousands of HP per hit and hit several times per second even with a 2h weapon.
Get solaels witch fire - this is a must have for any fire build. It’s actually quite a strong proc.
Wayward soul is good kind off but mostly for the OA nodes. you can’t have it all so I’ve taken it out.
Meteor (my recommendation) is kind of questionable. It does much less damage than you think for tier 3 devotion but the first 3 nodes are good. You can take those 5 points and get ghoul (great circuit breaker and sustain) or solemn watcher for DA. Ghoul is probably better but if your DA is very low solemn watcher maybe the best way to go
Edit: Also I forgot to mention blast shield is very powerful. You need to get that as well. Also Brute Force in the Shaman tree you need only one point to unlock feral hunger and max that. I forgot to edit that. It’s amazing for lightning but not for firebuilds. Let me know if this is all helpful I can give you some tips on a lightning build if you prefer lightning.