Hello, this will be a simplified farming guide. Please know that it is not necessarily the most efficient by any means, but I am making this guy to outline a way that I believe pretty much anyone will be able to follow. We do not have a way to easily get any seed in the game, etc. which is why this is necessary. If you follow the things in this guide you should be able to get 99 farming within two or three days.
Runelite Timers Plugin
On the righthand side of your client there is a small clock. Clicking it will open the timers panel. This is essential to farming. Become familiar with it, the sections we will be using are the ones for Herb Patches, Tree Patches, Fruit Tree Patches, Flower Patches, and Allotment Patches.
Obtaining Seeds & Seeds To Collect
The following are ways to obtain seeds and what seeds you should try to get your hands on to use
Master Farmer: This is good for getting any seeds. I highly recommend spending an hour or two here to get a decent stockpile.
Revenants: These drop a significant amount of Ranarr and Magic seeds.
Zulrah: This drops palm tree seeds, papaya tree seeds, magic seeds, toadflax seeds, torstol seeds, and spirit seeds.
Seeds you want to buy or otherwise obtain: Strawberries, Watermelons, Maple, Yew, Magic, Papaya tree, Palm tree, Limpwurt, Ranarr, Cadantine, Lantadyme, Dwarf weed, Torstol.
I highly recommend using bonus experience scrolls whenever possible for all skilling, but when you are harvesting (checking health) of tree or fruit tree seeds, you MUST have bonus XP active. This will get you additional hundreds of thousands of experience. Given how long trees take to grow, you do not want to waste it.
Keep in mind that during all of this you need to be using the Runelite plugin to know when things are done growing.
To get to farming locations, go to the teleport wizard, select "Skilling" on the side, and there are four locations. Ardougne, Canifis, Catherby, and Falador.
Level 1-32: Rake all of the patches at these farming locations. You will reach level 32 pretty quickly doing this.
At level 32 we will now actually begin planting things.
Tools you need to bring with you whenever farming: Rake, Spade, Seed dibber, gardening trowl, watering can (8). Purchase all of these from the skilling store.
Allotments, Flowers, Herbs
While farming, be on the lunar spellbook. Bring earths, natures, and astral runes. After planting something, always use the spell "Fertile soul" on it. With the exception of herbs, you also want to water them after you plant them in additional to using Fertile Soul. You can buy water cans (8) from the skilling store.
Each of the four locations I mentioned earlier that you can teleport to directly will have a flower, herb, and allotment patch. Familiarize yourself with the Farming guide (go to your stat tab and click on farming). Obviously you always want to plant the best thing for your level in each category.
Flowers: Plant limpwurts. These seeds are fairly common from master farmers and the experience they grant is great.
Allotments: Since you are starting at level 32, plant strawberries. Once you reach level 47, plant watermelons. The experience is really good.
Herbs: At level 32, you will begin with planting ranarrs. Look at the "Herbs" section of the farming guide and always plant the best one you can.
You will plant Limpwurts and Watermelons for the rest of your time farming, you will only upgrade your herb seeds as your levels go up.
Trees & Fruit Trees
In order to plant these, you need to turn them into a sapling. Buy empty plant pots, rake a farming patch, use the pots on the farming patch. This will fill them up with dirt. Add your seed to the pot plant, then water it. It is now a sapling that you can plant.
Trees: You will plant these in Falador park, Gnome Stronghold near the entrance to the slayer cave, Lumbridge behind the castle, and in the Varrock castle courtyard (east).
Fruit trees: You will plant these near the brimhaven docks (best way to get here is to teleport to brimhaven dungeon then leave it and run north), Catherby shore, Gnome stronghold directly north of agility course, outside the west side of Tree Gnome Village (teleport to red salamanders in skilling teleport and run east, look at your map you'll have to cross a bridge).
Trees: It is difficult to get any seeds below Magic other than from Wintertodt, so you will most likely only start planting at Magic. Remember to use the 50% bonus experience scrolls and these will grant a little over 1m experience.
Fruit Trees: At level 57 you can plant Papaya trees, and at level 68 palm trees. These are both dropped by zulrah.
I think this post has more than enough information for you to do farming. I am not going to entirely spoonfeed, everything else is common sense. If you believe anything should be added please include it in a comment or PM me and I will happily add it.