Non-boosting solution (however, I strongly suggest doing this in a boosting session, as this achievement is really tough):
You want to do this at Tier 1 because:
1) Only 7 enemies so lower chance of dying
2) Majority of tanks at lower tiers are light tanks
However, it is not so good as it seems. More lights means more enemies to kill. In other words, if the other team is full of lights you have to destroy every single enemy! It's almost impossible, unless you know the maps very well, know what to do and both your team and your enemy do not play very well. The second problem: T22 Proto. It's quite OP at lower tiers, especially for beginners who do not have so much credits. It lets you make few mistakes and guarantees that you won't get punished too badly for them. Don't be suprised if you see 6 T22 Protos + 1 light in battle.
There are four options. T22 Proto is quite obvious choice as you can rush into enemy and shoot with them. It is prefered choice for those who do not have credits for in-game equipment. However, it has huge disadvantage which is lack of gun depression. You won't be able to shoot from hill at Mines or downhill at Province. If you have free credits to spare you should go with another option.
Leichtraktor/T1 Cunningham/MS-1 - the most important part: buy binocular telescope and camo net! It gives you +25% view range and additional camo which are crucial at Tier 1. This is your key to effectiveness.
MS-1 is the slowest, 280m view range, 51mm penetration and 47 damage, Take T-18U package. This tank is the worst from three in my opinion, combination of slow speed (still higher than NC/FT/R.Otsu) and bad view range kills this tank. On the other side, you have wonderful gun which would be more than sufficient at Tier 2 battle.
Leichtraktor has medium speed, 310m view range, 40mm penetration and 36 damage. Take Leichtraktor II package. It's speed is OK and it has the highest view range. Combine it with camo and you have the best long range sniper which can defend itself even if left alone. Stay at the back if you can, it's not your front line soldier. Ninja style, shadow bush ranger, that is the LolTraktor.
T1 Cunningham is the fastest, 280m view range, 30mm penetration and 12 damage (machine gun). Take T1E5 M1933 package. View range is the same as in MS-1 but what really changes this tank into the beast is deadly combination of high speed, nice gun depression and mighty machine gun. This thing can smash any opponent which it encounters (maybe without NC and T22). You should pick any cover (rock/hill/building), go backwards, empty your clip and hide for reload. They wouldn't even know what hits them until it's too late. Do not use it as sniper in this combination, it is very inacurate at long distance and it cannot shoot over 400m. It is your Rambo tank, go closely, release your clip and watch the enemy die in blink of an eye.
Your worst enemy is of course T22 Proto. It looks impenetrable at first but you should aim at his turret, it's very weak. It also has problems with accuracy and gun depression so use them as your advantage and you should be able to kill Protos without any problem.
Medium 1 is tricky enemy. It has two types of guns, one is machine gun, which can kill almost two enemies at one clip but it loads very slowly. Use it as your advantage, wait until he runs out of ammo and then kill your defenseless enemy. The other gun is very inacurate but it has 70 average damage. This means he can kill any Tier 1 in two shoots. On the other side, it's big, extremely slow and thin-armoured.
NC-31/FT/R.Otsu are slow, well armoured, fast reloaders. Keep them on distance and try to aim at their hull. If you can, try to flank them and make circles around them. They rotate very slowly so you shouldn't have much problem killing them. Try not to fight with them frontally at very close distance, this is their turf.
MS-1 is similar but with better gun and is slightly faster. Its armour is also weaker. Shoot him from distance and abuse its terrible view range.
T1 Cunningham is probably your hardest to kill light. It is fast, has nice gun at close distance but it's not well armoured. People like to rush with it and go to front line. Use it as your advantage. Stay in bush, spot it and shoot. T1 won't be able to spot you and if it stops, it's dead.
Leichtraktor (a.k.a The LolTraktor). Probably hardest to spot enemy. Try to get close to him. Its gun and turret are at the back of the tank so you can stay behind a building, reverse a bit and shoot its turret without showing your tank. If the Traktor is hidden then go from cover to cover until you are very close. It's also quite big so you shouldn't have much problem killing it.
You have two different combinations. Province/Mines means that it is Tier 1 battle (in 90%). Different variations (rain, night) doesn't matter.
If at north side, LolTraktor/MS-1 stays at A4 and hides in bush. It should be able to snipe both middle and lighthouse/village. Adjust your position, if you see that no one is at village (right side of minimap) then make sure you can spot it. You can kill any attacker without being seen.
From south side stay at K4 and look at middle, K3 and look at lighthouse. Ignore the village, if something comes from that dirrection, go through K line to rocks close to your base. Use them as cover from hill/middle.
From any side Proto/T1 goes into middle and then uphill if it's safe. Watch middle if anythings shows there and try to use holes at side of this hill (D6/F6) to look at middle path (use rocks as cover from snipers). Remember to check village from hill. After that advance through middle and hope that no one took a scenic route through the lighthouse.
Proto/Cunningham go full speed to rocks closer to your base and near the enemies side (so if you start at left side go to H7, from right side go to G3-G4). After that go to the path leading uphill to enemies side and kill middle at the same time. At the top there are buildings and slight dip (so you would show only your turret while having enough gun depression to shoot). Abuse both of them. You can also go through F7 and E7 uphill if starting from left side, this way you can surprise your enemy. After your initial defenders are killed move forward and use terrain as cover. At left side go through line 1, at right side use the path).
Leichtraktor goes to G3 (left side) or D8 (right side), waits until bino starts working and snipe. Do not move unless you are seen.
Cunningham can also go to C3/H8, hide in bush and spot from this position. If you are in danger, hide behind a rock.
The rest of lights should stay either at D9 or at H2 and snipe.
If you get to any other map or you have less than 3 lights, play it normally and focus on winning the battle. If you get 3 lights then of course they are top priority. I did it at LTraktor with 5 lights at Province. Good luck!