First tip
Learn to farm under the turret
Melee: 2 tower hits 1 hit from you
Ranged: 1 hit from you then tower hit then 1 hit from you
This is important for getting enough gold, if you can get over 50% of the minions you should have more gold then any of your 2 opponents individually has.
However don't be greedy it's not worth losing half your health over a cannon minion ever!
Second tip
Try to soak as much XP as possible by staying with XP Soaking range
Range for minions is 1400 as far as i am aware.
Which is about as far as a max distance Sion E or Varus Q
As the solo laner you get 100% of total XP so you will level up faster
The average value of a level up in terms of power is worth over 500 gold ofc there are the level 6 spikes and other differences between champions which might make that value even greater.
Third tip
Get sustain and defense, and build according to your needs
This includes taking the Teleport summoner spell since you might have to back more often and you do not want them to kill your tower or lose too much XP
You will want to assess your sustain needs and the risk of an all in or tower dive attempt from your enemies and build accordingly
Because you might be farming with abilities more often and therefore run out of mana it can be useful to get some extra mana, thus grabbing a dorans ring on your first back can be useful even though you went to lane with a dorans shield or sword
Building that extra starter item or corrupting potion can help you last longer
If both of them do physical damage get some early armor if it's mixed you might want to consider going for health, and for magic damage you can get magic resistance
Consider your first item carefully, there are many items which can help you deal with the 2v1 scenario, i will give you a few examples
Will help you push and hold lane at no resource cost, it even provides sustain and resistances
However there are more benefits to be found in their component pieces
both are relatively cheap defensive choices
Raptors cloak even let's you get back to lane faster with the movement boosts near structures which will also help you avoid poke by dodging it or make you more slippery during dives
It even grants health regeneration for some sustain
Both components also have component items
which means that every time you go back to base you can pick up another piece of the final item even if you don't have much gold when you go back
Another fantastic item is
as it gives bulk & sustain
Other things to consider are how fast you can get back to lane when you have to back more often
can all help with that
Other things to consider
You won't need offense, not only is it unlikely that you will succeed 1v2 at least not in the laning phase, but you will gain offensive power from out leveling them anyway
One strategy used in high level play is a perfect example of this, sometimes when one of the laners gets an early kill from a gank or a play, the first thing they buy is a defensive item, usually just a cheap component piece like
or they grab defensive boots
What happens is that they are ahead in XP, they have the damage to kill their opponent because that is how they got that first kill in the first place but what the defensive item does is make it impossible for their opponent to kill them. it will also help out trade.
It's a matter of eliminating risks
What your jungler can do to help you is gank other lanes and snowball these instead. Or counter jungle and bully the enemy jungler out of his jungle.
In that case you win as long as you hold your own because you are technically ahead of either lane opponent and should be able to easily 1v1 either of them.
This means they cannot help the other lanes/jungler without you getting a massive advantage by either killing your opponent or zoning the remaining guy out of lane.
There are things you can do as a 2 man lane to mitigate gold/xp loss by using support items like
or letting one guy have most if not all of the gold similar to how botlane is played
Roaming and stealing jungle camps can help mitigate xp loss
Those are things to watch out for but you shouldn't encounter that much at level 25
Specific cases of synergy
And finally there is a lot of ''hidden'' synergy between certain items as well as champion kits etc you can use this to your advantage to get additional value out of your kit or out of items
I have used this today myself to get me out of a tough spot as i got camped really hard early on in a tough match up
I bought
on my mid lane
to get myself back into the game
Essentially what happened is my enemy lane swapped after hammering me down letting me face their botlane so they could get them ahead too and keep me down even further
I bought those items during that back and i ended up out pressuring my 2 opponents
You see i what happened is that
gives the harmony passive which makes mana regen hp regen,
gives 150% mana regen in jungle area so as soon as i stepped 2 feet out of lane into the nearest jungle entrance i gained massive amounts of sustain
I could even use one of my aoe spells over the wall on the jungle camp to leech 25hp per creep hit
Essentially i gained the sustain of 4x
+
from the synergy between these items :S and they where both components i needed for other items i was going to build so i gained over 1000 gold worth of value for free
I could simply run to the minion wave blast it with all my spells and run back to Jungle entrance hit the camp and fully sustain myself
I even managed to poke the enemy Ashe and Karma out of lane and their team had to come help them took them 3 people to keep me in check while i was quite a bit behind not 2 minutes before that :S