Here Basic Upgarding

I dont have much enchantin experience comparing to the rest of guys but ill write you basics.

You dont make B+++++. Avoid that, because later youll spend fortune on making fusers.

If you pay Real Money:

Get high durability gun F with lowest stats possible
Get some high min damage Ds and combine F with them so just min dmg goes D.
Get some high min damage Cs and repeat the process.
Get some high min damage Bs and repeat the process.

You should now have a gun with min dmg B and rest of stats at zero. Leave some Bs in vault for further fusing.

Start enchantin (thats the spot that more experienced guys come in so i wont explain coz i can do it wrong).

If you dont buy cards etc

You buy some BM.
You enchant the one with highest min dmg and lowest stats.
Rest of Bs stays for fusing.

Hope guys can take it from here.

Aqid:
Yes Murad is absolutly right. IF you are a paid member, start with an F, combine as many min dmg in as possible. Then you should have a good base weapon. This is weapon A, your base. Now you also need a fuser. This is weapon B

1. Make base (Weapon A) +10, put in ruby = AAA = +34 dmg
2. Make fuser (Weapon B) AAA, also min dmg.
3. Combine any other stat but make sure u dont increase much while combining (max dmg+1/hit+1/mp+50/crit+1/ mprec+1 etc).

Base is +0 again, repeat step 1-3 as many times as u like.

Step 1-3 is called "a reset". One reset will give you 34 dmg. You can calculate how many resets you need for your goal.