Mech mod safety. Three cells I would use are; (only buy batteries from a trusted source!) Sony VTC4, LG HB6 and the LG HG2.
If using a rebuildable use an ohm reader ( or a mod that displays resistance) to check your' resistance. I use Steam engines' website for coil building, .3 ohms is the lowest I would use on a 20 amp cell (lg HG2 is a 15-20 amp cell) and .2 for a 30 amp cell. Always use %80 percent of what the battery is rated at! Make sure the batteries have no mechanical damage; cuts, tears, discoloration on the wrap? Do not use that battery!
For the mod itself make sure the connections are clean and lock it when your' not using it. Check the fire button before you use it. Check to make sure the button is smooth throughout its travel and of course make sure it doesn't stick when you press it.
I'm sure I missed some things but they're is wealth of information on youtube and on here. Mechanical mods are safe as long as you follow the rules. Keep on vaping and have a good Christmas.