I have two bits of advice ...
There are many aspects to the trick. Certain things you can practice on your own, certain things you can't. Practising a trick which involves no mental work or misdirection, only moves and patter, is the sort of trick to learn in the first instance if you're not confident with presentation, misdirection, etc.
Practice tricks which you can take out. This way, you can practice presentation, and other things whilst you're performing something you know end to end. This trick or routine is the foundation on which you play with other things.
A classic example of a move which impossible practice, other than the setup and spreading, is the C*****c F***e. If you've got a trick which requires a true spectator selection from a hand held spread, practice that move at the same time. If they miss, not only have you the whole trick to back you up as normal, but you also have, if they miss by one, a K*y C**d as an out.
Why not, when you have controlled a card to somewhere, set up for a P**k or G*****e. Don't actually perform at first, just practice misdirection and decide as to whether or not you'd have got away with it. On another day, actually perform the above. It's an excellent out in itself. But if you fail, have an out for that sticky situation too.
With all this going on, on top of a solid set of tricks, you can confidently practice, out of context, many of the things that you can't on your own. You can certainly practice a bit of mentalism during a trick where the original trick is itself is the out.
The way I practice presentation is by actually speaking it, out loud, at the right volume and tone. I do this over and over until I get the rhythm and patter right. I do it to posters and photos. I do it to a camera, if the mood takes me. All that then remains is to get audience reaction and fine tune.
In the outside world, there is no room for bad moves and bad presentation, only room for minor adjustments and outs
So, to summarise, create a solid platform to practice on. Don't have too many things you're not confident in going on at once.