How does one...

[Xel_AI]

use MechJeb for interplanetary transfers?

[1of6Billion]

Get into solar orbit, 'transfer' shows planets instead of moons. Pick planet of choice. *fingers crossed*. Success is *NOT* guaranteed.

[Xel_AI]

Why?

Let's say if I have a awesome , high fuel rocket , why would that be?

[Nibb31]

MechJeb's method of transfer (going straight for solar orbit, then dealing with transfer), is far from optimal and can potentially lead to several years orbiting the sun before reaching the burn point for a transfer. You really want to wait until the planets are properly aligned before launching.

The best way to do a transfer for now is to use the protractor mod:

http://kerbalspaceprogram.com/forum/showthread.php/21544-17-Protractor-Rendez-Plugin-v-2-3-2-10-9-12

1) Wait on the launch pad and warp until the first value (θ) is near 0°, launch to orbit,

2) In orbit, warp until the 2nd value (È) is 0° (with Adjust selected) and burn prograde for your interplanetary transfer.

3) Half way through the journey, do a mid-course correction to reduce the Closest value until it intercepts the target's SOI.

[Xel_AI]

... Sounds tough.

I've lost my skill after not playing for months.....

Looks like it's back to MechJeb.

[Nibb31]

Erm... I kind of summed it up in 3 simple steps. It's not tough at all, and MechJeb isn't easier.

If you need to get your skills back, I suggest going for the Mun a couple of times before aiming for interplanetary flights.