The GTFO Maneuver

One of the first things you should learn about combat in Eve is that the only guaranteed move that will keep you safe is the GTFO maneuver, warping off to a station or POS is the most reliable way to deal with a bad situation. Or just picking a random celestial and warping towards it will save your ship, especially if it's only NPC's that are laying the hurt on you since they won't give chase. Once you're in warp you're essentially untouchable, which means that a would be pirate wants to kill your ship then they have to stop you warping off to safety - hence the existence of an array of high tech gizmos designed to stop other ships from warping off. Warp Disruptors and Warp Scramblers are an essential tool for any PVP pilots, be they pirates, militia or warlords in 0.0.

1. Dock At A Station, usually the one you just undocked from and realised that there's a bunch of hostiles waiting on the undock point. If you're unlucky the station will have already spat you out beyond docking radius, and you need to slowboat back into range. EIther way, you have to wait at least 30 seconds before you redock, and if you shoot at anyone then the docking manager will leave you outside until you stop shooting for 60 seconds.
2. Jump Through A Nearby Gate it's pretty common that you'll get the OhShitIt'sAGateCamp feeling moments before you get the OhShitICan'tWarp experience. You'll have 30 seconds of cloak, and a gate that's 12km away which if frequently the fastest way out, but don't be impatient, the gate won't accept you right way because of session timers, so take a few deep breaths before gunning at the gate. Again there's also a 60 second aggression timer, so don't do anything other than gun for the gate.
3. Warp Core Stabilizers are modules that take up low slots, these will counteract the effects of a warp disruptor, but you may need more than one of these depending on what the enemy is using, and they're completely ineffective against interdictors. However warp core stabilizers seriously nerf your ability to lock targets which really makes doing anything other than the GTFO maneuver a pain.
4. Move beyond warp disruptor range, If you're faster than the enemy then you can try running, Warp scramblers are pretty short range, typically less than 10km, Disruptors are good out to 25km or more for some ships.
5. Get Out Of Targeting Range and the enemy will be unable to keep you locked. There are very few cases where a warp disruptor will have longer range than a ships sensors, but applying sensor dampeners to an enemy can cut down their range quite significantly.
6. ECM can be used to break the enemies lock on you completely, either in the form of directed ECM, an ECM burst or ECM drones, it might take a few cycles, but it will work eventually.
7. Energy Neutralizers will suck the tackler's capacitor dry, leaving the enemy without power to keep their jamming equipment running, or maybe just shutting down their MWD for long enough to let you pull range.
8. Kill the ship tackling you, or at least do enough damage to make them perform the GTFO maneuver themselves. This is the first option that occurs to young pilots, but it's also pretty unlikely to work, after all, it's what the enemy is expecting, and they wouldn't have committed to the attack unless they were expecting to prevail.

The reason I'm bringing this up is that this is not something you're going to be able to decide when it happens, odds are you're going to find yourself scrambled and feel helpless, and unless you have friends nearby to help extricate you from your predicament. Options 1 and 2 are frequently forgotten or messed up my pilots who don't know about the various timers that prevent you jumping or docking. Most of the other options require you to have special modules fitted on your ship, which requires a level of planning usually filed away under 'cunning' and #8 sucks because unless you're able to tackle the aggressor he'll run off and you'll miss out on a killmail regardless of how awesome your combat prowess was.

So yeah, there are many ways to try an extricate yourself, but odds are if an enemy has commited to battle you're at a disadvantage, get on the hotline, call in whatever support you can, overheat all your modules, and when your structure is failing you make sure you spam warp to get your pod to safety so you can spend your insurance payout on something other than a new clone and implants.