Some hints for everyone :
Unfortunately, TCTD doesn't have "get-rich-quick" exploits that will allow you to level up quickly. However, there's a ton of opportunities to earn additional XP here and there, in addition to playing story and side missions. Here are some example activities to keep an eye out for while playing (or re-playing) the game:
Replay missions on higher difficulties.
Find and complete Side Missions
Complete random encounters
Locate ECHO sequences
The more you do, the more XP you'll earn. You can earn bonus XP by replaying missions on higher difficulty as well, so consider running each mission at least twice.
Dark Zone ranking
Your Dark Zone ranking will allow you access to better weapons, gear and resources both at vendors and when crafting. You can increase your DZ rank by killing enemies (and other rouge players), locating loot crates and completing objectives.
Keep in mind, however, that your DZ rank will go down if you die too often, so be careful about which enemies / players you choose to cross paths with.
Where to Find Loot
There are several ways to score better loot once you reach a higher level in The Division, but here are some pointers for scoring good gear early on.
Chelsea: Quarantine Zone Loot Stash
A few blocks south of your Base of Operations, near the corner of 8th and 24th is an alleyway between rows of apartment buildings. Make your way to the end of the alley and enter the contaminated building (marked with yellow hazard signs and sheeting).
This is also an encounter location, but more importantly each floor has rooms full of customization gear (hats, jackets, etc). There is also a lock pick door on the bottom floor containing a loot chest and some item packs.
Replay the Story Missions
After you've completed the available story missions for the first time, you can opt to replay them again on a higher difficulty. This results in more valuable mission rewards (typically a blue item or weapon, as opposed to the green one you'd receive for playing on Normal), and enemies that are more likely to drop better items.
Enemies will be more plentiful, deal more damage and have much greater HP than on normal. However, the end-mission "boss" will also drop a high-value item. To change a missions difficult, approach the starting area and enter the Mission Replay menu by pressing the Interaction button (pictured above).
Become a Master of Unlocking
While exploring the world and doing missions, players will occasionally come across a locked door that can only be opened with a lock pick. These rooms often have substantially better loot than players would regularly find out in the street.
Lock picks are dropped randomly by vanquished enemies, and can also be found in the loot satchels that are scattered around the map. If you're unsure whether or not you have any lock picks, check the Pouches tab of your Inventory.
When entering the contaminated area in MSG, you will die. Make your peace with that, then run through the door and directly to the chest at the far end. Open it and immediately loot the chest before you expire.
Legendaries for sale
There's a DZ Weapons Vendor located in the North-East region of DZ02, on the corner of East 38th St and Madison Ave. He has two High-End (legendary) weapons for sale, both the assault rifle "Caduceus" and the shotgun "Cassidy" cost about three thousand Dark Zone funds and require the buyer to have reached Dark Zone level twelve.
Dark Zone funds have a chance to be dropped by any hostile NPC in the Dark Zone. The funds are also rewarded to players who land the killing blow on other players, or as a bonus for outlasting the rogue agent timer.
Dark Zone Keys
Similar to picking locks, while in the Dark Zone you will sometimes find special chests that can only be opened with a Dark Zone Key.
These can be obtained as random drops from enemies, or by killing a rogue agent with keys in their possession. In order to open these crates, you must also meet the DZ rank requirement for the chest (typically 8 or 10 - more info on that below).
Big Box, Big Score
Keep an eye out for large containers, both in the PvE-only section of midtown and in the Dark Zone. A good rule of thumb is "the larger the box, the better its contents." Mid-size crates will usually contain green items, while large strongboxes and cases will contain blue.
Increase Your DZ Rank
Your Dark Zone Rank determines not only where you're able to explore in the DZ, but also what types of chests you can open.
Most of the smaller chests have either no rank requirement, or a required DZR of 5. Larger chests, such as the long weapon crates or large storage trunks, require higher DZ levels (8 & 10, respectively).
Other Tips, Tricks, and Secrets
There are several locations accessible in the early stages of The Division that are chock full of useful items and loot. Be sure to visit them with each of your characters to unlock new customization items and potentially useful loo
Help those in need
Often, while patrolling the streets, you'll encounter civilians asking for aid. If you happen to have what they're asking for on hand (med kits, water, food, etc), be sure to give it to them. Not only will you earn some easy XP, but these NPCs will usually drop a reward - oftentimes in the form of a new customization item.
Don't be afraid to enter a stranger's home! Odds are, if you find yourself able to enter an abandoned apartment, there's something worthwhile waiting for you inside.
Some skills, such as the Sticky Bomb, can be used in a couple of different ways. If you hold down the Skill button assigned to that ability, you'll be able to aim and toss the device where you want it. If, however, you want to place the device and set a trap, simply press the Skill button once.