Lane pushing:
This is the term used when your team is pushing forward, usually with the help of minions (to take the damage), to destroy the two towers, the phoenix, and eventually the titan.
The essential concept here, though, is to know when to push forward and when to back off.
It is obviously best when your team just completed a deicide (complete wipe of the enemy team). With no one to contest you, any tower will go down quickly, without damage to your team, as long as you use the minion wave. However, depending on how healthy your team is, you may try to get a few hits on a tower even in the presence of 1-2 enemies (especially if they're low on health and afraid of dying). Just be cognizant of how much damage you and your team can take from the tower, as the tower will ignore minions and target YOU the second you hit an enemy within its boundary.
However, I've also been on many a team that had already gotten a tower down, then got a deicide, pushed and destroyed the 2nd tower, maybe got the phoenix, and tried to go for broke with the Titan. NONONO. You NEED to watch the enemy respawn timers! I've gotten flamed for backing off when they rush the titan with a death wish. If you're aware and your team isn't paying attention, tell them to back off...VRR "Retreat!" Otherwise, the enemy team is going to do to you what you JUST DID to them.
The best strategy is to ALWAYS watch the respawn timers, destroy what you can safely, and then back off to regroup. Heal up, wait for any dead allies to respawn, and maybe incorporate lane freezing (see below) until your team is ready to go again.
Lane freezing:
A simple example of this is as follows:
It's still early game, and all towers are still standing, but your team has hit the enemy hard...your side has 10 kills, they have 3, and they are scared and demoralized. So what do they do? Camp from the relative safety of their tower, clearing minions only when they're at the border of the tower.
Don't let them get easy gold. Instead, freeze the lane. The concept here is to
let both sides' minions attack each other without intervention/damage from your team. So you back off to about the mid-point between the two towers where the minion wave meets, where your proximity allows you to gain XP/gold every time an enemy minion dies.
Don't attack the minions! If the enemy wants some of that too, they're going to have to come out.
Past the point of drawing them out, you can even try boxing them in by pressuring them with your presence. Stand in
front of the minion wave when they meet, and have your team use poke abilities and general presence to keep them away.
You should do this EVERY TIME a team camps their tower/phoenix. It's a slower and safer method, but it'll pay off.
The idea behind suicide backing is to replace the minion wave and
tank the tower/phoenix, allowing your team to damage/destroy it at an opportune time. At the same time,
your death without the intervention of the enemy denies them XP/gold. The proper execution of this would be if the majority of the following conditions are met:
- The one suicide backing has built up a small hoard of gold (a minimum to buy at least 1 complete item, usually in the range of 2-3k gold).
- The enemies are all dead, or there are only (e.g.) 1 or 2, and they're low health and no threat to damage tag you and chance dying (more on that below).
- The majority of your team is alive, or is respawning shortly, rendering your death acceptable...they should be able to at least hold their own tower by playing conservatively, while waiting for you to respawn.
Although it might be impressive to have a score of 12 kills, 0 deaths, and 25 assists, holding on to 5k+ gold does no good for your team.
Strategic dying (but maybe
not dying!) includes suicide backing, but can also be used in different ways by select gods with appropriate abilities. Some examples:
- You're
Loki, and everyone but you has been killed, while the enemy has only lost 1. They're pushing forward with the minion wave to blow through your 2nd tower and maybe your phoenix before everyone respawns. Use his 
Vanish ability to sneak through their lines, appearing behind them and running toward their tower. There's inevitably at least 1 enemy that is greedy and will go after you, with a possibility of drawing more of them away from their push. Although you're destined to die (unless you can sneak BACK), you've given your team some extra time to respawn and recover.
- You're
Mercury, and your last push has almost killed their titan. The phoenix is still down for a bit, and both teams are fighting relatively in the center of the map. Use a full range 
Sonic Boom to blow through their team, get behind them, and attempt to finish off the titan before they can catch you. A bit risky, especially if they have a god that can ult and close the gap (e.g. 
Thor, 
Thanatos, 
Apollo), but can be worth it.
- You're Apollo, and your team is being pushed under your tower. You've taken a lot of damage, have no lifesteal, and the second you step out from behind the tower, you know you're going to be toast. So you stay back, doing NOTHING, and you're no freaking good to your team. Instead, go
Across The Sky and land near an enemy tower. You'll die, but you won't give them the XP/gold, and when you respawn, you'll be able to contribute to the fight again. Maybe this time, you'll get that 
Bloodforge or maybe buy that 
Salvation to help your whole team. =P
This is a counter to suicide backing. If you're in a situation where you are the only one alive on your team, and they have 3+ still alive on their team, they may push to damage/destroy your tower. In damage tagging, the minimum you have to do is
hit them once with a damaging ability or basic attack. If they then die to the tower, you get the kill, the XP, and the gold, instead of letting it go to the ether. You should attempt this only if the majority of the following conditions are met:
- You've got enough health that if you get hit a couple of times, you're not likely to die.
- You've got some form of CC or escape ability.
- The enemy taking the damage isn't close to full health, and/or an enemy healer is not present.
You don't want to try this if they're all pretty much at full health. Even if you hit them, your chances of getting a kill are low, and you're exposing yourself to a potential gank unnecessarily. Also consider the potential presence of an enemy healer, like
Ra or
Hel. They may be able to keep their teammates alive, turning
you into
dead.
General tips:
Watcher's Gift
Ymir
Hades
Ares
Purification Beads
Celestial Legion Helm
Bastet
Pounce
Razor Whip
Divine Light
Celestial Beam
Solar Blessing
Serqet
Rama
Agni
He Bo
Tectonic Rift
Mjolnir's Attunement
Jotunn's Wrath
Hide of the Urchin
Predator
Venomous Bite
Cocoon
Night Crawler
Insatiable Hunger
Arachne
Butcher Blades
Regurgitate
Unbound Runes
Unchained
Seething Howl
Brutalize
Ragnarok
Marked for Death
Incense
Lash
Destruction
Assassinate
Odin
Scales of Fate
Swift Vengeance
Lunge
Slice and Dice
Gungnir's Might
Retribution
Raven Shout
Divine Judgement
Harvester of Souls
Death Scythe
Scent of Death
Soul Reap
Hovering Death
The Executioner
Qin's Sais
Spear of the Magus
Obsidian Shard
Greater Purification
Greater Aegis
Divine Ruin
Brawler's Beat Stick
As
Curious if anyone's tried him as a tank, and what your build was.
Regarding building tanky when there are no tanks on your team, I just finished a match where I did just that as
Build was a bit funky, and the match was a bit weird, but on a general basis, Nemesis seemed to be a pretty good choice.
The enemy team had 4 phys and 1 magical (
Anyway, it worked out in the end. I died twice, got 3 kills, assisted on a good amount, and took the most damage. After completing
Biggest thing I noticed with
I even got a "thanks for the carry" from a teammate after the game, though
Now I'm itching to see how the other assassins might fare as substitute tanks!