If you want Brexit... In this case, it's pretty simple - vote Tory. The Brexit party (and UKIP) don't have any meaningful chance in any seat in Scotland, so that would be a wasted vote, and the SNP, Lib Dems, and Labour are all in favour of a second referendum, and thus stopping it. So if you want Brexit, you have one choice.
If you want Independence... Again, a very simple case - vote SNP. The Greens have no meaningful chance in any seat in Scotland, and everyone else is opposed.
If you want both... This is now actually a pretty small group - about a third of people who voted Yes in 2014 did so because they really wanted to be out of the EU, and now that the UK is heading that way most of them no longer actually want independence. But if you do want both, decide which you want more (or want first), and vote according to the questions above.
If you don't want either... This is the more complex case, and depends on who currently holds your constituency.
- If your seat is currently held by a Labour or Lib Dem MP, it's easy - vote for the party that holds the seat.
- If your seat is currently held by an SNP MP, the choice is slightly tricky. Basically, you should vote for whichever of Labour or the Lib Dems did better last time, except for two caveats. If you are absolutely determined to avoid Brexit and willing to sacrifice independence to achieve that, your best bet is to vote SNP. Alternately, if you're absolutely determined to avoid independence and are willing to sacrifice Brexit to achieve that, and the Tories came second last time, then you should vote Tory.
- If your seat is currently held by a Tory MP, you unfortunately don't really have any good choices - neither the Lib Dems or Labour party have any real chance of taking any of those seats, so you're stuck. If you're absolutely determined to avoid one of the two, and are willing to sacrifice the other to achieve it, then hold your nose and vote accordingly. If not, I guess you should vote for whoever came third last time, and accept your vote is probably wasted.