I've rerolled on FFXI a lot(particularly in it's later days) so give this a read.
First: Kudos for picking to main WHM.
WHM is one of the best starting jobs for new/returning players...
1) You dont need a ton of gear and progress to start being useful.
2) Most other people hate playing healers so you have less competition for your role.
3) The other jobs who can heal can not do it nearly as easily as a whm.
Melee While Leveling WHM on a new character:
First, for now you need to set aside the idea of WHM being a healer or even a mage. Obviously you picked whm for that reason but youll get your fill of healing at 99. You should keep in mind that while leveling a new character(no matter what job) is that your most likely better off doing part of the DPS. Especially if you dont really have many decent trust. You are better off in most cases using a whm trust to main heal and you just focus on melee. One big point to be made about using trust to heal is that you can periodically resummon them to refill their MP. Something you can't do for your WHM.
Priority for gear is the highest DMG clubs you can get.
Hammers are the best melee variation of clubs so stick with them. Pay attention to the actual damage value of your club rather than it's level. Generally there isn't much real good gear for low level healing and you should just focus on picking up what you can for melee gear. Honestly the hammer is the only big deal, just at least occasionally upgrade armor for sake of defense.
Sub Jobs:
It would do you well to unlock NIN for Dual-Wield or at least DNC(which is a much easier option).
Weaponskills:
Skillchains were modified in the more recent past. As well as a lot of older WS's.
So chaining is ever more than before, an efficient way to level quick and
with a club you will see a significant DPS boost from
focusing more on skillchaining rather than zerging.
Your first good WS is
Seraph Strike.
It's fTP starts a little more than 2x and it scales very evenly from 1~3k. So there's little loss from holding TP for chains unless your sitting on 3k. Alignment is Impaction which happens to close and open for a lot of common WS's. Most notably
liquifaction > impaction = fusion Its worth noting that at low to mid levels, closing fusion with seraph strike effectively makes most dps trust(available to a new player) look awful.
The next good WS is
True Strike which is both detonation and impaction. It is also both a melee dmg WS(seraph strike is magic dmg). Its dmg doesnt increase from TP but instead it's accuracy does. It's crit rate is 100% so get some accuracy food and it should serve you well(sushi).
At level 67(and 220 club skill) you'll get the creme dela creme,
Hexa Strike. A 6 hit, critical hit WS with the Fusion skillchain property. It really needs no explanation.
Trusts:
I dont know which trusts you got. Whether you had been active during a trust campaign, your missions, etc. I'll cover whats mostly available at a bare minimum. One thing to always remember is trusts dont level up when you do. You have to resummon them to bring them up to your level. This can make a big difference if you are grinding a lot of levels in the same area.
https://www.bg-wiki.com/bg/Category:Trust#Alter_Egos_by_Role
The best early game trusts (that come to mind and i'm sure i'll miss some)
DPS trusts:
*a = A trust who tries to close skillchains and otherwise wont use tp till it reaches 3k.
*b = Obtained by Records of Eminence objective: Tutorial > Basics
Ayame: She's a sam and has a simple useful logic. She remembers your most recent WS and will try to open a SC for it if you have 1000+ TP. She doesnt have Shoha or Rana which means she doesnt have fragmentation or gravitation. Obtained from Bastok mission progress.
SemihLafihna: An amazing easy to obtain DPS. A rng who truly embodies the meaning of glass cannon. Unfortunately she doesnt understand that sometimes and is prone to AOE WS's at times. Try to avoid crowds of mobs with her. You can easily burn through levels with just you and her as DD's. (*a) Obtained from Windy Mission progression.
Tenzen Not bad but not as good as Semih. (*a) (*b)
Shantotto II Login campaign trust but worth mentioning in case you got her. A nuker and the absolute best magic burster. Has good DPS even without burst opportunities.
Adelheid The easiest trust to get that magic bursts, mostly helixes for high DoTs. Shes not the best at it but she can bring more to the table than a mediocre dd when you have your chaining down.(*b)
Zeid II Pretty solid DD. Uses stun sometimes. (a*) RoV mission progress
Tanks:
Valaineral: typically he will be your best tank trust for awhile. (*b)
Volker A WAR tank with better DPS than other wars, typically keeps hate if dmg isnt spiking. Not a bad option for adding extra dps if you got him. Bastok missions.
Healers
Rule of thumb. Be in either Yoran-oran or Apururu's unity. They are the best trust healers. Both have auto regain(TP generation) and exclusively use a WS called knott which recovers mp. At times they dont really like to use it for what ever reason. This behavior particularly happens at low levels and gets better as levels increase. kinda...
Yoran-Oran The more MP efficient of the two. Doesnt use curagas, doesnt cast haste.
Apururu Can get trigger happy with MP. Uses curagas, uses haste.
Support Roles
There arent many options when starting fresh. Check the section in the link above. Silvie is a great option that is availible by joining her unity. But you sacrifice the best WHMs.
Btw...
don't use <stal> for healing. Use f-keys to party select and write macros with <stpc>. stal is intended for controller users... draw back of f-key/stpc is if you dont use windower or ashita you cant bind alt+f1-6 and ctrl+f1-6 for alliance selection. Automatically configured in the init's for both apps.
If you dont use it you really should...
http://www.windower.net/
The only excuse for not using windower is being an ashita user. But ashita is not very newbie friendly
:P
Familiarize yourself with Weapons Attributes and Skillchains
https://www.bg-wiki.com/bg/Category:Weapon_Skills
https://ffxiclopedia.fandom.com/wiki/Category:Skillchains
https://www.bg-wiki.com/bg/Skillchain
Also this, I never used it but I hear a lot of ppl say they did.
https://www.bg-wiki.com/bg/Quickstart_1-119_Guide