Any advice?

I'm gonna have a go at changing my front shocks myself. They're still working but the mechanic who done the warrant says they're leaking.I boughtshocks and axle stands and spring compressors. Where am I going to go wromg and f it up! 94 nissan sentra fwd n14 . I've never done shocks before.

To do anything to any vehicle, do it properly, step by step, according to the manufacturer (Nissan).

Here is the link to your cars complete service manual.
http://www.freepdfmanual.com/2009/05/07/1990-nissan-pulsar-sunny-b13-n14-maintenance-repair-and-troubleshooting-manual

There are two versions, and they are a big download. But as with every workshop manual, Im sure under the "Front Axle and Front Suspension" section listed, you will have every single step for disassmbly and assembly, as well as exploded view diagrams of every part, for changing your front shocks, all according to Nissans specifications. Well worth the download. Just dont try printing the whole thing!

I suggest you do it according to that diagram and nothing will go wrong, its also a good thing to learn. Worst case scenario, find a local mechanic, explain where your stuck and tell him theres 2 boxes of beers in it for him if he can come around help you after work. Good luck

Did you buy the whole strut (including the lower platform for the spring) or just an insert (a long thin cylinder)! A strut is easier to fit but cost more, the insert is cheaper but requires more work. If the insert, then you need to make sure you don't damage the strut when disassembling/reassembling it. Otherwise, compressing and releasing the spring will be the toughest part of the job. In a workshop this is usually done with an air tool and you'll see why when you attempt to compress the spring. It is possible without air tools but requires much patience and effort. A ratcheting ring spanner of the appropriate size would help a lot. Be careful as compressed springs contain a large amount of potential energy waiting to rip your head off.

Also, pump the shock up and down about a dozen times before fitting. If you don't the shocks will be rock hard and make you nauseous within 5 mins of driving, and have to be removed, pumped up and down a dozen times then refitted.
Edit: I know rock hard sounds good but in this case it's not.
Not at all.

#4 never had a problem with new shocks being rock hard before fitting, oil only shocks need priming because they have been stored on there side and you need to get the air to the top, gas shocks dont need priming as a rule, If they are rock hard when you drive they will be rock hard when you try to move them by hand.

What the hell are you on about! This is why these message boards can be so dangerous cos people that have no idea try to give advice.