Phase One: You Need a Black Hole
If there isn't one handy, bring a lot of stars together in one place and squeeze them within the Schwarzchild Radius for the whole heap of stars. You'll need about 1,000 stars like our sun to make a hole big enough to work with.
(Schwarzchild's critical black hole radius is equal to an object's mass multiplied by twice the constant of gravity and divided by the speed of light squared).
Phase Two: Pop Through The Wormhole
Drive your spaceship carefully into the Black Hole, through the space/time tunnel (or wormhole) and out the other end. You will now be in a different place and a different time. Find a large mass (e.g. a big planet) to dangle in front of the wormhole's mouth.
(Check whether the planet is inhabited by sentient beings. Inter-galactic law may require relocation strategies to be in place prior to dangle).
Phase Three: Pull The Wormhole along
Dangling the planet in front of the wormhole, tow it back to where you started - gravity will cause the wormhole to follow like a donkey following a carrot. As soon as both ends of the wormhole are near one another drive round and round in a circle.
Phase Four: Twist The Ends of The Wormhole
This is where it gets tricky (as opposed to merely difficult).
You will recall that Einstein predicted gravitational time dilation in 1907 as part of his Theory of Relativity. This phenomenon has since been confirmed by experiment (see American Physical Society: moving clocks run slow relative to one another) so it ought to work, fingers crossed, touch wood etc. but you will need to be patient.
Whilst one wormhole mouth is circling around, time is passing more slowly for it. So keep twisting for as long as you want, as fast as you need, to make a time difference between the two ends of the wormhole. Each twist increases the time difference and the faster the twisting is done, the greater the difference. When you stop, and have parked the moving mouth down next to the original black hole, the mouth you moved will now be a set distance in time behind the other mouth (the Black Hole). Don't worry; each end of the wormhole will have the same gravitational influence so they will balance each other out and you won't get dragged into a continuum paradox.
Phase Five: Using Your Time Machine
Suppose you have set a time difference of a year. Drive in one mouth and you come out of the other a year in the future. Go round as often as you like, jumping another year on each occasion. To get home, go round the other way, jumping backward one year on each journey.
Important: You can never go back further than the time when you built the Black Hole. If you do, then you will be in another universe with a different time line, where it would be possible for you to murder your own grandfather and still be alive in the universe where you started from. But things might not be quite the 'same'. Better to stay in the universe where you are, so you only have one time line to remember and your mum won't be quite so upset with you.