When starting a mission or crucible match or anything, you will want to take advantage of having the best guns for your mission or whatever. Having the right guns can help you run through your mission a lot easier without having to sit there and take out a enemy's shield (which all destiny players know...is annoying).
Step 1: Figure Out What Your Going to Do
Decide wether your going to want to do crucible, vanguard strikes, Vault of Glass, Crotas End or anything else you want to do.
Step 2: Find the Best Guns
Your going to want to find the best guns to accomplish and finish your strike, mission crucible match or whatever your doing.
Step 3: Gun Damages
You will want to find the type of damages are best for whatever your doing. Some guns do certain damage which can help in defeating some enemy's.
Step 4: Start Up Whatever Your Doing
You then want to start up your mission, strike or whatever your doing. I would highly advise to have a fireteam if your going to want to do The Vault of Glass, weekly nightfall, weekly heroic strike (level 30) or anything that's harder like that.
Step 5: Begin Playing
Start playing and have fun with your guns when you complete whatever your doing!