Yep, you’ve been punctuating it wrong all these years. We know, because we see this mistake all the time. It’s probably the most common error we see.
Here’s an example of how not to punctuate when using however:
There’s usually no need to book a reservation, however please let us know in advance if you’re coming as part of a large group.
This sentence has what’s known in the grammar trade as a comma splice. And the comma splice is up there with the grocer’s (grocers’?) apostrophe as the grammar crime most likely to elicit tuts of derision from the punctuation-conscious reader.
To avoid being branded a comma splice criminal, you have three options.
1. Create two sentences
Your best option for punctuating the above sentence would be to break it into two sentences, using a full stop, a capital letter, and then a comma:
There’s usually no need to book a reservation. However, please let us know in advance if you’re coming as part of a large group.
Remember: Full stop. Cap. Comma.
2. Use but