Efficient ways to train:

If you don't mind how long it will take you to raise farming (for example you could do other skills in between and it would even out) then a good idea may be to plant fruit trees. They're the best XP for money and time besides calquats. When you're able to do calquats too, at 72, 12k XP for 20k is wicked. Sadly there's only one calquat patch and they take forever to grow, but it's really worth it. You can do basic trees (like willows) on the side if you can afford to, but the XP you get from them is not even close to what you get from fruit trees so they're only worth investing in if you plan on doing two or three runs a day - three being the most you can fit in unless you're pulling an all nighter or something.

Depending on how much you can afford to spend on farming, I would recommend orange trees as a minimum, or pineapple plants. Orange tree seeds are roughly 2k each (I think) and the last time I bought pineapple seeds they were about 15k each. This makes orange trees the more preferable option for efficiency, but pineapple plants will get the job done more quickly. Anything above them, I consider to be breaking the bank.

Unavoidably, farming is going to cost you a lot of money, so the idea is really just minimising that cost. Because of this, farming is not a skill that you can really power-train unless you chain farm the allotments which even then costs a small fortune and is not worth the effort.

Mining: If you can use the Lunar humidify spell or have the water tiara from one of the newer quests, mine granite. The experience rate for granite is only 40K/hr compared to 35k/hr for iron but you don't click as much with granite. Either way you go, I can help you find good mining spots if you need help.

Herblore: Serum 207 is the cheapest from when you can make them to 99, slow xp though. For decent XP, super defence pots are the least lossy (for all decent xp pots with guyable ingredients).

Farming: Not my Area of expertise, fruit and tree seeds for good xp (costly), Herbs for cheap slow xp, a mix of both for a bit of both, your call.

Summoning: All the fast ways are expensive. Just kill stuff and save every single charm, i do it via slayer, but nechs/dust devils are the best i've found without paying a lot of cash for ice bursts, if you have cash to waste then burst rock lobsters or melee waterfiends (not nice). This is very expensive no matter what, unless you want to do it all on gold charms, which would take about 40 years.

Agil: Wildy to 70, ape atoll from thereon in.

Mining: Yes, granite. Lunar spell "Humidify" helps for pouch refills.

When I thinkof efficient, I think of skill relationships as well. The biggest problem I see here is that you are only taking xp into account with things like power mining granite. You need gp to train summoning, farming, and herblore yet get zero gp per hour of granite mining.

Granite mining: 45k xp per hour
Gold mining: 33k mining per hour

Mine granite for 2 hours is 90k mining xp
Mine gold for 1.5 hours, smelting and selling for a half hour is:
50k mining, 45k smithing, and 150kgp.

With arzinian mines, you can even mine more gold per hour. That 150k buys quite a bit of herblore xp and seeds. With summoning beasts of burder and the ring/whistle method of mining gold it is even faster.

I trained my farming and herblore into the 80s by doing herb runs 4-6 times a day. Develope a system that works for you. I can hit all 5 herb patches in five minutes now. With smapdragon seeds I get upwards of 100kgp per trip.

Some people might say don't let them die, but do the math yourself. 15% die, so you have the chance of getting 100% of 1 herb patch or 85% of 5 patches. You can still make money just letting stuff die. Tree payments are also a money loser, because only 1 in 10 dies. The value of the payment for 10 trees is more than the cost of a seed, especially in the case of yews and magics, the worst trees to pay for.

Agility - Just do the wildy course. Bring buckets of strawberries and an anti poison. The revs poison you. if one appears, try and just log out. you can do it by going through the tube, or up and down a ladder. Then log in on another server and leave the rev to kill whoever is left on the course (hehe).

Summoning - Might as well wait for the update to come out and see what happens. I would also say that over half of my levels are from tears as well. One thing to focus on are spirit spiders. Combine that with snapdragon farming, and you have easy seconds to make super restores. They well well and are the most profit of all seeds. Spider carcasses are a bargain at 300gp in the GE.