A journal is not a notebook for jotting down wins and losses: it is the tool that turns experience into learning. Without data, your conclusions rely on memory, which always remembers the wins better.
What to record on every trade
Date, instrument, direction, entry, stop, target, size and the result in R and in money. Add the reason for entry (which setup it was), your emotional state and, if you can, a chart screenshot. The easier it is to record, the more consistent you will be.
The metrics that matter
Win rate, average R per trade, profit factor (gross profit ÷ gross loss) and maximum losing streak. A positive average R and a profit factor above 1 indicate a profitable strategy; the maximum losing streak tells you how much risk you need to be able to withstand.
How many trades you need
With fewer than 30 trades results are very noisy: a good or bad streak fools you. Evaluate your strategy with samples of at least 50 to 100 trades before changing anything important.